I do roll up my racing sails, but the cruising sails I've folded for 18 years.  They're quite baggy now after all these years but the folding never caused any problems.  That mabe because I seldom flake the sail in exactly the same spots before folding them up. And when the winds pick up enough that it's time to reduce sail it sure helps to have the sails always in the same arrangement in the bag.

John