I wash the fabric for two reasons - one, I want it clean and free of anything that might be on it, and two, I want to preshrink it before I sew with it. I don't want any shrinking surprises when I wash the finished product. When I use the jelly rolls I will not prewash them because I don't think there is enough yardage and I am concerned the fabric will distort to much. However, when I do this top I will not prewash the backing either, hoping when the quilt is completed and washed things will shrink at the same percentage. Does this make sense to you?