Alex Anderson said to NEVER use sheets for backing if you are using good quality fabric in the front of your quilt. The difference in quality alone will make it NOT wear well. After going to all the work on the front, why skimp on the back. There are plenty of sales on fabric out there to pick up large chunks for backing and still keep the quality of your quilt top. Of course if you used really cheap fabric on the quilt top, then I guess it doesn't matter because the whole thing will not wear well over time.