I use to prewash, now I don't. The handling of unwashed fabric is so nice during the piecing process. I do wash the quilt once I have completed it, whether it is a gift, or not. I put a "color catcher" in the washer and any loose dyes are absorbed by it. It also removes any "dirt" the quilt received while under construction. Machine drying shrinks the batting (if it is going to) and sets the stitches. That's what works for me.