So when is a SUT really needed?

@jay73 ,

a few answers to your Q.

1. A true step up has no cord and does not plug in. Its a stand alone unit. 

2. A step up is not a step up. There are varying degrees of bandwidth and gain levels. 

3. when is it needed? depends on how low the power supply noise floor (ripple and signal to noise ratio) is on your phono stage and how much output a given cart has. The lower the output level on an MC cart, the more likely a step up will help. 

Once a person decides on a step up there are so many options from super inexpensive to outrageously expensive. 

I dove down that hole a few years ago, and could not easily return to a phono stage with no step up. 

Faustuss, I think you need to look up “diatribe”.

Policing this forum is a thankless task.

I echo what @viridian said. His statement clearly explains. 
I alone can’t do without SUT. I like how it sounds.. I tried Parasound jc3+, Sutherland 20/20, Ayre, Lab12 master, MoFi master.. simple SUT just makes my setup sing.. I have a Koetsu Urishi Wajima with Clearaudi Master reference turntable. 

"I like how it sounds."  That about sums it up.  You use a SUT with an MM phono stage for your LOMC cartridge, if you prefer that result to using your LOMC with any other amplification device, which might include a higher gain phono stage that in and of itself provides sufficient gain or an outboard active gain stage ("head amplifier"), which for the OP's benefit is a plug-in device that adds only gain, not RIAA equalization, to the output of the LOMC. The output of the head amplifier then must be fed into an MM phono stage for RIAA correction and for added gain, just as in the case of using a SUT.  In recent years (to the OP), the idea of amplifying the current (not the voltage) output of an LOMC has come into vogue among some.  So now you have the additional choices of using an outboard gain stage that operates on current gain and that then puts out voltage to drive an MM stage or a current-driven phono stage that affords lots of voltage gain at its output sufficent to drive the downstream linestage or direct to an amplifier.  It's a bit bewildering, and there is no perfect answer. You have to try a few of the alternatives for yourself and make your own decision. Moreover, one doesn't know what else you (OP) do or don't know, so please ask more questions.

It really gets down to trying different things.  In my years of doing this I have acquired MM, MC, MI, low output, high output, (I don't even know how many cartridges I have) two phono stages one very expensive tube one, and one moderately expensive solid state one, two SUTs, one silver wire and one copper.  I can't tell you what combination is "best" depends on the record, my mood I suppose.  Elliott correctly pointed out to me in a previous post that people just have to try things.  The truth of the matter is that I am happy as a clam with a MM and always have been.  My absolute best is a LOMI > SUT > tube phono stage.  But I am just as satisfied listening to a recently acquired MM > SS phono stage that cost one twentieth as much.  The thing is, though, in order to gain that perspective you have to experience different things.  There is no substitute for experience.