Call me a sourpuss if you have to, but I think that messing with the knobs and faders in a documentary is mostly so the camera has something interesting to look at.  Most music t.v. shows would have the same impact as a radio broadcast or a magazine article if our guy just stared dead-eyed ahead and delivered his 2 cents.
 
I dunno.  Sometimes it's fun to hear the mix get all messed up in ways that I've never heard before.  It's just cool seeing some of my favorite old rock tunes all discombobulated.