Bands should just learn to shut up in general during sound check, only play when the FOH asks you to play, and stop when they ask you to. You can have a successful soundcheck in 5 minutes that way.
Having 5 band members each playing random guitar store bullshit at the same time for 20 minutes doesn't help anyone do anything and is just a waste of everyone's time, I can't stand it when bands waste soundcheck time.