I guess I may be overly cautious, but I always wash my fabric first. I want to know what's going into my quilt before I begin. I don't have to worry about colors bleeding from one fabric to another (You can read all the horror stories here about that!), and the fabric will have done the majority of shrinking, so there won't be uneven puckering or shrinkage later. I know the fabric is truly clean, too. I even wash small pieces by placing them in a mesh bag to prevent unraveling and wadding up.