I think its gotta be just interesting on the theoretical side around learning/cognition. Otherwise yeah, its like learning exactly how salty something is when you taste it: not a total waste of time maybe, but not directly beneficial for you as the cook.

In school, at least when I was there, ear training was a combination of recognizing harmony, rhythm, and simple melodies with an arbitrary key, ontop of, of course, sight singing. It is of course quite sufficient to have this skill with all of that, but hardly necessary!

It's not beneficial at all. Don't do it. The only music that will sound "right" is autotuned crap from the most boring types of music. Anything interesting will sound "out of tune".