I wash pre-cuts but I wouldn't really wash something that I had cut to size already. If you're just looking to get the sizing out, you could try a piece or two washing in cold water in the sink & then lying flat to dry. Other than cheapy Hobby Lobby fabrics and a few from JAF, I usually don't have problems with shrinking, but if you put them in the machine, they are likely to fray just a bit (maybe 1/8" to 1/4" tops) and that will throw everything off.
I don't pre-wash for fear things will shrink after they're quilted -- with the exception of flannel -- but rather because (1) I want as many chemicals out as possible since I make baby quilts, and (2) I have some difficulty with applique work due to the sizing (e.g., WonderUnder will not adhere properly if there is sizing in the fabric).