Pre-washing is a very individual thing. Some swear by pe-washing and some swear by not pre-washing. Many people here have said they've mixed pre-washed and not washed with good results. You can pre-wash pre-cut strips by hand and hang to dry with very little fraying. The one time I worked with a jelly roll, I soaked and rinsed by hand, then spun in the machine in a garment bag, then hung to dry. I pre-wash everything because I prefer to have shrinkage take place before stitching, to having it happen after stitching, and I don't mind taking the time to do it.