I piece all my backs since my favorite size is 48 - 54 wide x 72 long. I like to do a vertical seam off side, not exactly in the center. If it is "off", no one can tell if it is meant to be off. Nothing exact, either 10 or 12 from one side, or roughly a third of the back. If you try to center it, everyone can tell if it is not centered. I use either leftover blocks in a column or strips or squares of the front fabrics. In my mind, I can think that if it needs repaired, someone can take a fabric from the back with the same wear and washings and fix the front.