In high school Home Ec classes, we learned to prewash fabrics before cutting for garment making (who wants to make something that doesn't fit after that first wash?). When I started quilting, I continued to prewash the fabrics (no precuts then) and haven't changed my mind after 30+ years. I measure fabrics before and after laundering and find that even a complete line of coordinating fabric shrinks differently, Other than the (only) batik quilt I made last year (a note was attached with fabric NOT to prewash so gave friend a box of color catchers), I have continued to prewash everything before cutting for a quilt (haven't made wall hangings), admitting I don't use jelly rolls so no experience there; I've washed charms on delicate cycle. That Home Ec teacher also stressed 'sew-press-sew-press' and it definitely makes the difference on a finished product, whether it be a garment or a quilt. NOTE: I still have guilt feelings about not prewashing those batiks!!! To each his own, but prewashing is my comfort level so I've not mixed washed and not-washed fabrics in a quilt.