Most rooms don’t need acoustical treatment.

Why?  Because acoustical treatments presented are in virtually empty rooms. Unrealistic.

my rooms have furniture and clutter.  These rooms don’t really have a need for treatment.  It’s snake oil, voodoo science.  
So why is accoustical panels gonna help?  No one can answer this, most have no clue.
I agree! All of my systems have been setup in cluttered rooms! Yet the sense of stereo space, depth and impact was undiminished!
Surprise- you're right. Sort of. Most rooms do have lots of different kinds of furniture in lots of different places, which do serve to diffuse and absorb and break up a lot of the worst flutter echo one would have in an empty room.  

But that is about it. And notice, it's all random. Because of this it does no good to talk about "most rooms" because no one really cares about "most" they care about "their" room. As soon as we move from the hypothetical home of the scoundrel to the particular home of the individual then acoustic treatment can suddenly matter a lot. 

The physics and acoustics of standard acoustical treatment are very well understood. At the end of the envelope where extreme performance is paramount the science verges into art. But the science behind things like first reflections, arrival times, and bass attenuation traps is solid. It works. As does a lot of stuff much harder to explain. But you might want to keep in mind that just because we cannot explain why something works, does not mean it does not in fact work. Happens all the time. Can you explain how your car works? Yet it does. 

Hear, hear MC. Absolutely right.

And even acousticians and psycho-acousticians admit there's much they don't know or can't explain. But this is true in every field, including the ones that collectively put men on the moon. 
Mofojo is right.  We do know how a car works.  On the other hand, we don't know why someone prefers a blue one to a red one, or a Camry to a Prius or why anyone  likes the Fiat 500.  (Well, maybe in some cases we do--like why I prefer my 88 Volvo wagon to anything built in the last twenty years that would cost me 30 or 40x as much).
You wouldn’t happen to have a blue 88 Volvo Wagon and live in West Mi would you? 
Room treatment can be tricky. Unless one can  determine what and where specific (!) problems are occurring and apply treatments to treat those specific problems at those specific locations, one might make things worse.
The "knowing how a car works" is still a valid analogy.  While many have a general understanding of how engines, brakes and steering work, very few of us are mechanical engineers and have a detailed understanding of the design details and why certain choices were made. And keep in mind that even engineers tend to work in very specialized areas -- you don't hand the development of the car's suspension to the engine team.   

The same is true with many of the technical devices we use daily. One does not need to be an electric engineer or app programmer to use our cell phones or laptops.  

The same is true of acoustics and room treatment. It is a discipline that is well understood by the specialists in that area. However, what is obvious to them may be much less so to the rest of us.  But that is the beauty of audio as a hobby -- it is easy to experiment.  If you get good results, great! If you make things worse, they can generally be easily undone.  And no one is is danger or has their life ruined by the process. 
it all depends on your expectations for good sound. who is to say what you like, or what you will put up with.

lots of my top musical moments have zero to do with the fidelity, and everything to do with who i was with and what i was doing. top down, cruising the 101 in the early morning with my girlfriend on spring break in 71’, playing ’Here Comes The Sun’ on my 8 track is my top musical moment. who cared how it sounded? it was the moment.

OTOH if you do care about musical truth and fidelity then the room matters, and playing room roulette regarding getting lucky naturally does not work for many. symphony halls are not casually assembled for a reason. domestic rooms operate with the laws of physics also (slightly different than large halls for sure).

and at low volumes the room is not very relevant; but if you want to listen at live music volumes, then the room will really rear it's ugly head and make the experience horrible. you blame it on the recording, or the system, but it's mostly the room that cannot handle scale or dynamics.

here are some educational video’s if you actually want to learn about the subject.

if you have any doubt on this subject, go to any audio show and walk into 30 rooms and see if they all accidently sound good. if you love them all then find another hobby. this one is not relevant for you.
my friend doesn’t have acoustic treatments in his room

but then again, he is almost deaf

i hear quite well, i need 'em in my room for my system to sound really good
I have the Hifi in our living room and as you can see (from the following pic) room treatment wasn't really needed once the room was properly furnished with our favorite things.

Even for near listening most room need not only passive acoustic treatment but more active controls...I know that by experience and experiments... i know that because i read many times that near listening can spare me acoustic treatment and it is false in my room and physics dont change with room....But many people have not experience this fact because the listening in a moderately big room is not the same experience than in a smaller one....Then near listening in s small room is NOT AT ALL near listening in a way bigger room....

Acoustic is more complex than what we read in audio thread...

A  room is NOT a passive reflecting set of surfaces for the waves of sound to boucing off or be absorbed or being diffused... Like acoustical companies suggest to sell their materials... This is only half the story... A room can be activated and is a potential sets of different heterogeneous pressurized zones.... Helmholtz science...

Acoustic is more powerful than most upgrade...

No speakers at any price could shine in a bad room or even in an ordinary room....
Re the OP,
"It’s snake oil, voodoo science."
Absurd falsehood. Every toom is different, and furniture and objects induce their own changes to the acoustical properties of the sound waves in the listening room, but acoustics are not voodoo science. If you could see soundwaves you would know this. Wind tunnel testing or a wave tank are demonstrations of wave theory and how the waves interact with objects they flow over—you can see it. Bass loading is a very common problem in untreated rooms, especially small ones. I am working with GIK Acoustics to tune my new-ish room now and tame the bass, reflections, etc.

The AVroomservice guy is smart, and acoustical engineer by training iirc, and has good videos and info on his site.

Jim Smith in his excellent book "Get Better Sound" talks about the room, and how spending lots of money on your hi-fi without treating the room (and setting up the speakers properly too), at least on a basic level, means you’ll never hear the full potential of your system. A modest system in a well set up room will often sound better than a more expensive system in a room that is untreated, especially if the room has inherent problems ( dimensions, ceiling height/shape, large/many windows, too live or too dead a floor etc). A room can be over-treated too, rendering it dead like an anechoic chamber. It's always a balance between none and too much. 
Why?  Because acoustical treatments presented are in virtually empty rooms. Unrealistic.
Not sure if you are making a statement or advising others. But you have also provided the reason why they are not needed, as it depends on a case-2-case basis. Yeah, your room is furnished and does not need treatment. My room is purpose built and was empty to begin with. A simple change in moving couple of treatments made profound positive changes in my case.
BTW, most forums also don't need duplicate threads. You have another thread on the same topic. Might want to remove it.
@patrickdowns,I have to agree with you.OP is clueless. But I think he is new on the forums and might be trying to "get attention".

Roger that. A quick search of the topic here would help him/her. I just searched "Jim Smith" and got lots of hits:

jumia - Member since Jan 04, 2021

Is this yours @milpai?

Are you happy with the GIK panels and bass traps? I am waiting for their designer to get back to me with suggestions. This is a well-sorted out room. I probably have too much stuff in mine (bookcase, computer desk in the corner) but it’s my man cave too!
Lamps on end tables reduce room modes.

Sums up the understanding of acoustic treatment 
some are commenting on.
Pretending acoustic treatments universally do not help is to assume that the amount of clutter, rugs, drapes, blinds, bookshelves, upholstery, art on the walls, etc. is uniform in every room.  If you have "enough decor" to not require any extra treatments, then great - but rest-assured there are many rooms that will in fact benefit. You can have someone clap from each of your speaker positions, and if you hear reverberation or sound decay from your listening position, then you might want to consider treatments, whether those treatments are "decor" or specific acoustic treatments. If you do not add treatment, then you can expect that the sound leaving your speakers will be subject to the same "added color" that you heard around the test clap.  
I dont think "normal" rooms have 4 inch thick bass traps in the corners which DOES help tremendously if you value great non boom bass. Other stuff is great as well, one of the least snake oil things in this hobby which there is plenty of. 
@dekay long as you keep all your remotes on your belt in that space you're good to go....;)
"my rooms have furniture and clutter."

Why do you assume that my room is cluttered?

(It is not)

Jumia was more observant than me though as...

I never noticed the "window shelves" or the ceiling for that matter.

We lost track of a "cable guy" a few months ago (starting to smell funny in here) and come to think of it I have not seen my wife and one of our cats for a few days now.

I use a fanny pack pack for the remotes (like real men do).

Fanny pack:

There are two types of audiophiles ... those who have never tried acoustic treatments and 'think' their system sounds great. And those who have treated their rooms and 'know' their system sounds better than before.
It took me two years to find a house with a good room and if you find one of those acoustical treatment is not needed at all and when you put uneven items in the room it just keeps getting better.
This has to be top tier trolling. 
Voodoo science? The results of adding treatments is easily seen in measurements. 
I placed pillows behind my speakers, at first reflection points, and scattered a few more around in my small home theater room. My soundstage is more present and dynamic, and the center of the soundstage is well represented despite a 52” lcd. 

The challenge now is coming up with a more permanent solution. I’m talking to GIK. 

I’m not sure I accurately described the difference before vs after, but I find myself listening to more music. I’m thankful for some of you keeping the treatment discussion alive. 

Give it a shot, it’s free. 
When you furnish your room, when you put curtains on the windows and decide on cloth furniture instead of leather, when you put up shelves and install rugs or carpet, you are acoustically treating your room whether you know it or not, whether you think you are or not. As has been said over and over, everything matters. If most rooms don’t need acoustic treatments it’s because most rooms (correctly or incorrectly) already are.
You can make it more or less acceptable but if you want the best sound you got to treat the room, though I call it to tune the room. Sounds more correctly, less mechanical. Room as a musical instrument. 
Millercarbon- What does “As soon as we move from the hypothetical home of the scoundrel to the particular home of the individual then acoustic treatment can suddenly matter a lot.”

On what planet do you exist? Why was it important to include the word “scoundrel”? Are you trying to come off as some kind of “Audio Sage”

I have recently purchased 2 GIK Bass Traps; the difference in sound is amazing.
It is not pointless. Many people have their systems in living rooms and cannot do their best in terms of making it the best acoustical place.
Erik doesn’t play analog and listens to Luxman integrated. Not very high standards. In fact...alright, I said enough.
@inna no, a discussion of acoustic treatments isn’t pointless, the original post is, and sounds like a kenjit post...
@dekay LMAO

I don't have acoustical treatments because my setup is not in a dedicated room, unfortunately. I recognized the need when I did one of those sound tests that went from 1000hz to 0. On the way down, I could hear at the low end where my components provide strong bass and little bass and also where the room resonates (as did things in the room, which I removed).
I set up my room using acoustical principals but without using specialized products. I don't have any glazed pictures in the room. The art on my walls are wood carvings and tapestries. It's relatively balanced. I've done this so many timesI feel I'm getting a 6th sense about getting good sound out of a room. What I've noticed is that old homes with thicker, stiffer walls do much better than the thin drywall in newer homes. Older, concrete-based acoustic ceilings are gold.
Is it the best case scenario? No. But it works well enough to fool me. Now, I've had better rooms to deal with but I do also enjoy looking at the room I listen in as well. It's part of the equation for me.

Most treatment, to me, looks ill. And, let's be honest, the sound/signal does not care if it's a specialized product or not. I imagine even the best treated rooms using the latest tech aren't a perfect exploitation of their potential.

Oh, dekay.....*sigh*  'Fanny packs' (aka 'butt bags') are So 20th Cen....

Spouse remembered a wool vest I wore decades ago (until the dry cleaner shrunk it to fit a 3 yr. old).....and got me this recently...
Comfy, but I'm prone to 'frisking' myself trying to find whatever I'm trying to find...and you'll note it has the Least pockets of their products....

My 'listening space' is a little better than you've illustrated (no search parties required as yet), but is cluttered enough that I'm looking forward to the day it becomes obsolete due to a relocation.
But, since I run DEQ, it sounds good to my drain bamage....for now. *S*

Something I've considered, since I'm an omni fan, is to investigate trying these as a surface over an acoustic 'blanket/panel'....
...if only to avoid the 'padded cell' look of an extreme acoustic treatment, and keeping in mine that omnis 'like' reflection...properly attended to, of course....;)

Thinking 'outside the box' first requires one to accept the existence of 'the box'...
I've tended to lean into a 'mobius loop' sort of reality, myself...*G*
Another ’off no wall in particular’....

sand them all -or- sand the mall? Either makes sense to me, but just obliquely curious....*G* ;)

'asv', for me, is just my variant on AVL (thinking that all caps would be too big of a hint....*L*)
Sum all untreated rooms and they average out to have random placements of objects made of random materials.

Ampa style setups need close to nothing. No back wall and tapered side walls and ceiling, no reflection points..

Setting up kitty corner, eliminates a lot of the normal treatment ideas and again the reflection points diminish. Room decay rates are much quicker.

Clutter counts :-) There are ways to reduce the UGLY as$ wall treatments diffusers, dust collecting stuff. Foam is hard to keep clean.

CURTIANS work and look the best to me..

It's easy to tune a room and liven it up just a bit with a curtain pulled open or closed a little more.. No studio looks for me.. 

"So why is accoustical panels gonna help?"   

Are trying to say :

So, why are acoustical panels going to help ?

Truth, but only if you want to justify your room multipurpose optimisation. However, if you have dedicated room for critical listening, the room where you want to dissolve in your music without distracting factors, you’ll need treatment. 

It's 'sand them all'. 

Back in design school, I was in line in the shop to return some tools. A friend of mine walks up and asks the guy in front of me if he should sand just one of the pieces of wood for a project.
The guy responds by saying 'just sand them all'.
Then they both pause as a light flickers in their nerdy eyes before they burst out in laughter.

My name is Sandamal. It's a perfect phonetical pronunciation of my name. And once again, as it has so many times, my name has betrayed me.

Bottom line it does not matter. We all spent serious money on our systems yet The chances of even 1% being the same is rare. All that matters is our own ears and the preference of sound that we prefer or are reaching towards. I have heard inexpensive systems that sound great and really expensive systems that do not. I am an advocate of some room treatments. That is because it sounds great to me and several other people.