I usually don't prewash. I like to use cotton batting and love the look of everything shrinking together. I do tend to buy the more expensive fabrics and will prewash reds if I am using them with whites (I don't use many reds) I always, always prewash flannel fabrics because even if you buy the real expensive ones, they all shrink differently. I also use the color catchers when prewashing or washing a finished quilt. I wash all quilts after finishing before I give them away. (exception would be wall hanging that usually never get washed) I prefer working with unwashed fabrics.