I always prewash except for precuts. coming from being a clothing maker and prewashing everything for shrinkage... nothing worse the taking your time doing a great job on a nice new outfit and then the first washing it shrinks and doesn't fit any more. just a waste. also as said in previous posts the little buggies that sometimes get in the fabric and do their thing. also I don't like the sizing they put in things and the dyes sometimes cause skin problems and I like the smell of my washing detergents and starch (thanks Blondie for the recipe). I also line dry all fabric never put in the dryer , but then I rarely use my dryer except in the winter when I can't get out and hang things. Just me quirky. Happy sewing