From Keith Richards' autobiography, Life:
What you're looking for is where the sounds just melt into one another and you've got that beat behind it, and the rest of it just has to squirm and roll its way through. If you have it all separated, it's insipid. What you're looking for is power and force without volume -- an inner power. A way to bring together what everyone in that room is doing and make one sound. So it's not two guitars, piano, bass and drums, it's one thing, not five. You're there to create one thing.