Good idea to starch even if you plan to wash it afterwards. Keeps it flat while quilting. I also use a 1/2" seam allowance on the backing fabric and starch the seams open and flat to help with quilting over them. Unless it's flannel, minkee or fleece - still do the 1/2" seam allowance but use spray basting on the seams (underside) then press them open/flat with my fingers - don't like quilting over a lot of thickness on the backing.