Music is about communication... it isn't just something that maybe physically sounds good or orally sounds interesting; it's something far, far deeper than that.
Exceptions are not always the proof of the old rule; they can also be the harbinger of a new one.
Our feeling is that the most important thing on a set is that actors have enough confidence to try different things. If there's stress or tension, they won't go out on a limb because they won't want to embarrass themselves if they don't feel completely comfortable.