Every nuance of a person's experience of song, whether they are performing or in audience, has a meaningful role in the event. The existence of performer and listener is intrinsic to the art. Good music can be perceived effortlessly, but not without engaging on some level with what the music means. Where it comes from and what it evokes.
I have found some engineers to embrace and develop a certain vigilance. It's a practical mindset to cope with the multitude of control points in a studio, but the big picture is that they are attempting to understand and coach all the nuances of experience at play, moment by moment. If it's a good day then there may be something special happening in the studio, and the challenge is always to discover the nuances that comprise this, to foster, capture, and connect them to the listener.
The details of how this gets done though can get a little stoopid...