I would never piece a back. It scares me when I am happily quilting to feel a difference in the stitch. I think something is going wrong in the bottom of the quilt, to find out it was a seam. Either my machine is very sensitive to changes or my relationship to my machine is so close that I can tell something is going on. So, if I am making a big quilt that will be in a show I tend to get 108 inches backing fabric. But most of my quilts are wall hanging that will be sold, never wider than 44 inches, so those get backed with regular fabric. Large quilts that will be used on daily basis, watched, slept on by the dog, and maybe washed more often that once a week get a sheet as backing. Never had a problem. I try to get a set for the bed I will be making the quilt for, and use the flat sheet for the back. When The bed is made it has fitted, sheets and the back of the quilt all matching. I have sold several as a set like this and my customers are very happy.