I took a long arm class this summer at our state show. The teacher was explaining that some people use two layers of batting for quilts that will be in a show, usually wool with a cotton, and with the batting closest to the backing it is usually turned a quarter turn. She explains this helps to provide the stiffness for them to hang for the show, hang straight and not have any waves in it. And as mentioned in this thread, to enhance your stitch appearance. She also explained the added weight as well as the stiffness and did not recommend it for a bed quilt, simply because of the drape, or lack of actually.