I really find it tedious the prep before and after. Most of the time when I have done it I found the fabric really did not hardly shrink so found it a waste of my time so now I only do it if I plan to embroider or if the fabric smells. You can test for bleeding without washing an entire piece. For precuts they might shrink so much that they may be not the required size that you need or fray badly. Those are just a few reasons. Fabric has more body and is also easier to cut when not washed