I seem to be a dissenter--I frequently use flannel as backs and rarely prewash. In more than 20 years, the warranty to replace worn quilts has never been used! I will prewash if it is bargain store quality. When that shrinks it is the weight I want it to be. I believe that the quilting holds it in place or that it shrinks equally with the rest of the quilt. I like to think I'm efficient rather than lazy. 8^)