Pre washing is a personal decision based on fabric type & circumstances. Batiks, for example, are already pre-shrunk, but some people like to pre-wash to remove excess dye. I personally rarely pre-wash. I don't have time enough in my life to quilt much less pre-wash & iron my fabric before hand LOL. But I can understand prewashing. it does make your quilts flatter. I personally like the shrunken look of quilts that are not prewashed so that the batting & fabric shrinks all at once. If I mix batiks & regular cottons, or regular fabrics & flannel, I would pre-wash to make all the fabrics "the same". whatever you decide, be confident & informed in your decision. You can pre-wash sometimes for a particular quilt & not for another, too.