The look of the finished quilt matters more to me than being economical with the fabric.
Good for you! It's really annoying to have a quilt just a few inches too small to fit a backing. I usually buy wide backing to save me the hassle for a small quilt and piece a backing for a big quilt. I do pieced backing this way. The LA can turn the quilt to have the seams going the best way to quilt it.
http://www.reddawn.net/quilt/backings.htm