I was told that you should always use spray starch if you pre-wash your fabrics, but you don't need to if you don't. I guess because pre-washing takes out the sizing that the manufacturers include in their process. Also, Harriet Hargrave recommends using a very light spray starch when you are pressing while you are constructing your blocks. Your seams lay flatter and make it much easier to stitch in the ditch when you are quilting.
If you do use spray starch, you need to wash the quilt if it isn't going to be used right away, because it attracts bugs.