I prewash yardage, but never precuts. Some do and say it works out, but really, it can (and most likely will) be a nightmare if you do. They fray, tangle, shrink, get wrinkled, etc., etc.
One main advantage of precuts is to make quilting easier, not harder. So go ahead and use them without prewashing. Very few fabrics bleed today due to a much better dying process, but if you are concerned, then when the quilt is finished, throw a Color Catcher in while washing and that will take care of any bleeding that might occur.
