I do not prewash, for the most part. As long as you quilt the layers moderately, batting controls shrinkage when you wash a quilt. Fabrics can shrink very differently from each other when washed alone. That difference really doesn't matter after moderate quilting has joined the fabrics to the batting.
Shrinkage of individual fabrics does matter if you tie a quilt, especially if the ties are not close together. It might also affect a quilt where the quilting lines are far apart (say the 10" allowed by Warm and Natural batting). In those cases, the fabric isn't tied to the batting sufficiently for the batting to control fabric shrinkage.
Even flannels (which are notorious for sometimes shrinking many inches!!!) do not require prewashing as long as you are careful to keep the quilting lines close together (I would say 3" apart would be the max distance for flannels).