"Perhaps Arthur Murray should teach that, instead of "This dance is for silver dancers only. If you don't know what you're doing, get off the floor NOW!", which is exactly what I heard at a studio near us. It wasn't an AM, but it was run by former AM instructors."
That may sound harsh, but it really only takes a handfull of slow or unpredictable moving couples to choke up a floor to the point where the advanced dancers will either be sitting out, tutoring beginners, or crashing into couples they can't see while trying to avoid the ones they could. Designating certain dances for different types of traffic flow makes a lot of sense in that situation.