What happens if you don't turn the paint when it's being stored for a while is simple. The weight of the paintball, and the weight of all it's little buddies that are on top of it, press down onto the same spot continuously. This wil cause small dents to appear in the shell, and also the paint will become somewhat oval shaped, instead of round. All this adds up to low consistency in velocity, because of irregular shapes in paint, which in turn leads to inaccuracy. Also it severely increases the chances of paint going bluagh in the barrel.
So keep turning the stuff. Or do as I do. Don't store paint, shoot it instead.