I might be totally insane or very brave. I never prewash. I dislike ironing of wrinkled fabric so much that if I had to do it all the time, I would not enjoy the quilting process and would probably quit. I doubt that, but I really don't like washing and ironing new fabric and like the feel of the not washed fabric.
I bought a batik jelly roll from a board member. It was not prewashed. I made a beautiful braid lap quilt with it and some other batiks that I purchased (joanne's and lqs). When I was finished I washed it in cold water with three color catchers and LOTS of water. It turned out beautiful. This quilt was mine to keep.
Am I recommending my method...nope. I am just sharing my experience.