What exactly is critical listening? Who does it?

OP, only you can decide if you want to do critical listening--if so, when and why.

I’ve done a lot of it, specifically:

• When I’m writing a review of a headphone, amp or DAC (to post on an audio board ... not a professional reviewer)
• When I’m writing descriptions of the sound of a given DAC, preamp, amp, pair of speakers
• When I get a new (or new-to-me used) component and first hear it in my system
• Or when I hear someone else’s system/equipment

Critical listening is an entirely different mindset from casual or enjoyment listening--the kind I do most often. Critical listening requires less emotion and more analysis, ie, What exactly am I hearing? How can I describe what I’m hearing in words someone else can understand?

Critical listening isn’t fun, but sometimes it’s necessary. And one’s hearing, like any other brain activity, can be practiced and improved, resulting in more focus and awareness of what is being perceived. For example, time spent listening critically helps me indirectly (yet significantly) when I listen to unfamiliar music and try to put it in the perspective of music known to me (perhaps beloved by me). It could be a jazz cut or a classical performance. There’s a halo effect with critical listening, at least for me; sometimes it helps even when I’m not consciously listening critically.

So I'm really having trouble with what exactly is the definition of critical listening, this what OP asked in original post.

Some state that listening to the sound of one's system is critical listening, this inferior to a mode where one transcends the sound of their system  and/or eliminates consciousness of it's sound quality or qualities. 

So, my question is why is this a superior mode of listening, what makes it inherently superior? And why is consciousness of sound quality or qualities necessarily a critical mode of listening? And then we have the music and the performance of that music, is there not some level of critical listening in that?  We all have favorite artists, genres of music , favored performances of that music. So somehow we magically escape critical listening when we just listen to the music, some magical spell transports us to this world of no judgment, comparison, consciousness. 

My take is whenever we are listening INTENTLY  to music reproduced over high end systems we are inherently in critical listening mode, this applicable to the music, performance of that music and the sound quality or qualities of our systems. I assume we all got into high end audio in order to more realistically present music in our home environment, we wish to feel a closer connection to the artists and their performance of music, this requires critical attention being paid. Casual listening on the other hand is not critical listening, our attention is diverted to other things. Critical listening is listening with full attention, is not necessarily judgmental or doesn't have to be judgemental. Critical listening is listening with heightened senses, this is not a bad thing. 

I always listen critically because I want to know what the system is doing well, what could use improvement, and maybe most importantly, what the engineer is trying to convey (and maybe not convey?).

I want to hear all those small changes that would go unnoticed to most.

I want to hear the engineer "touch" the pan pot.

When a singer doubles their voice, barely audibly, in the background, I want to be able to hear that for what it is, and where it is.

On overdubs, I want to hear the "punch in" when it occurs.

I want to hear the buzz of the amps from the performance, though I could do without the snare rattle.

I want to hear when the noise gate opens and closes.

I want to hear the "easter eggs" many of which will never be picked up through casual listening on a lesser system.

The list goes on, but these are the things that I find enjoyable and keep the music fresh and most are only picked up through critical listening.

BTW, if it matters, I am a retired consultant/scientist who specialized in noise and air quality studies for CEQA compliance.

Critical listening is the gateway to whatever is there on the other side of the fence.

Of course I’m going to critically evaluate components that I’m spending decent money on, and then when it comes through the door I’m gonna be very critical to ensure it does everything I was hoping for.

I’m gonna listen to all kinds of music that I’m familiar with critically evaluating the changes and hope to be hearing with a new purchase.

When I was younger, I never had the awareness to listen very very carefully however I was very mindful of how well music filled the room vs crappier systems which were disappointing.  

I think you can balance critical listening and other types of enjoyment at the same time.  Unfortunately, we all have an instilled discipline within us that prevents us from avoiding this ongoing critique of everything we do and see. 

Presently, I’m done buying all this audio stuff aside from potentially upgrading speakers. So the critical side of the mission is fading away, thankfully.  Maybe I have to buy a car and I have to now critically evaluate all the new electronics and stupid digitized Dashboard which is horrifying, I don’t like a having an iPad embedded in the dashboard. 

I'd suggest critical listening can be broken down into two sub modes, one judgemental, the other not. Judgmental mode is for evaluation, listening to sound quality, qualities in order to compare, contrast to some reference.  The other mode of critical listening is intentionally careful listening which should bring about a sense of heightened consciousness in which music, artistic performance and sound quality, qualities all serve to maintain undivided attention to this single activity of listening to music on a high end system. Music, artistic performance and sound quality should all have great salience such there should be a conscious acknowledgment and appreciation for each.