I don't typically use pieces/fabric from the front of my quilts. I, too, work mostly on one quilt at a time. I also only buy for projects - not stash. Generally I will buy the backing fabric when purchasing for the top but not always. I do like my tops and backs to coordinate but not particularly 'match'. I purchased wide backing for the first time just a few weeks ago. This was for tops made by a friend who had not managed to find backing fabric. My LQS had nothing that I felt was appropriate for the tops and/or did not have enough of the fabric that was needed. Granted, these were queen/king size quilts.
That was my first experience with wide backings and I can't say I was disappointed. It may end up being my new 'go to' solution for the bed sized quilts I generally make.