A friend of mine once had to pull all of the brown M&Ms out of a bowl for a band. I can't say that they thought it was worth it, but we also followed all of the other rules in that contract when booking that band. We hired a different band the next year because that was a real nuisance.
Van Halen had his choice of cities and venues; a test like this is perfect for weeding down to the ones who will take the all the other seemingly-random-but-actually-vitally-important requirements around stage and equipment setup seriously.
It doesn't work for the musician hired just to have someone playing.
Yeah, we agreed once, but nominally you would prefer to have repeat business. I assume that there are venues that either buy pre-made no-brown-M&M mixes or just don't book bands with that clause.
Van Halen got away with it because it's Van Halen.
