I only prewash if I feel a reason to. If I am making clothing, always, but for a quilt I only wash it if it comes from a thrift shop (only sheets, as in my area nothing else is out there) Once in a while a fabric will be stiff enough that I want to see what it is without all the sizing. I don't care about shrinkage, because my batting is going to shrink anyway - and that's what I want it to do. I have had only one fabric that bled in about a dozen years of quilting, so I take my chances.