I don't prewash my fabric but, if I did, I would definitely starch it before cutting. Spray starch has always been problematic for me. I starch large pieces of fabric (especially backings) by mixing up a solution of Sta-Flo liquid laundry starch and water and "painting" it on with a large wall painting brush until the fabric is saturated. I then toss the fabric in the dryer and later iron with steam. For backing fabric I use a 1:1 solution but for preparing fabrics for piecing a top I would probably use a 1:3 (weaker) solution.
The advantage of starch is that it stabilizes the fabric so it doesn't stretch or distort as you handle it. Cuts are more accurate and piecing is more accurate. Heavily starching the backing fabric for machine quilting helps ensure no tucks or puckers.