I don't prewash no matter what batting I am using. I do, however, check any suspicious fabrics for colorfastness.
If you are planning to tie your quilt or quilt it with lines very far apart, then you may want to prewash fabrics for shrinkage. With normal quilting lines, prewashing to shrink fabrics is unnecessary. This is because after quilting it is the batting that controls shrinkage. A fabric will not be able to shrink more than the batting. (This does not hold true if quilting lines are, say 10" apart, because that is enough area for the fabric to shrink independently of the batting.)