I usually cut backing piece and insert something pieced to get more width. I like to use up orphan blocks or leftover scraps from the front. If you are sending your quilt to a longarmer, ask her/him if they have any preferences on seams. I prefer mine vertical if possible. I am also a sucker for a pieced back (I HATE to piece them, but LOVE them when they are done! Go figure!) Piecing backs appeals to my thriftier side. I like to use up the scrappy stuff, so I can save the longer yardage for big quilts or borders.