I do prewash all my fabrics in hot water with Synthrapol. Why because if you look at the fabric, all fabric is not created equal. Even those you purchase from the fabric store. Even those that come from (example only) Debby Mumm to Ro Gregg and many others. Have you ever sat to sew an had those little threads continuely pop out and have to cut before the whole row ravels. Fabrics come in tight weave to lesser weave and therefore need to be treated so that the possibility of little hand or big hands accidently hitting the hot on the washer cycle is covered. It's no big deal to iron afterwards and before cutting. I have had many shop owners say they don't wash their fabric. Each to her own.