Is it actually used when playing or just as an embouchure/aperture exercise?

It’s absolutely a valid technique to be used as often as possible as long as the sound of the articulation is appropriate for the style of music being played. I am sitting here running some tunes for a gig I am doing with an Australian band called The Cat Empire and have been taking particular note of where and when I use it; it is often!!!

I’m finding that I’m able to pop out double Gs through mouth compression easier than actually playing the note. I’m guessing that’s a good thing as it’s teaching me how to properly use my aperture and tongue. I’m hoping that it will become easier to sound the note.