I longarm quilt for others and it does not matter to ME which way YOU PIECE your quilt back or how many pieces you use.
What's important is that you use 1/2" seams (NOT 1/4"...it's too skimpy). Put smaller pieces in the center of the quilt back...not at the edges. If you put them along the edge, there is the possibility that only a small amount of the smaller piece will end up on the back.
What's important, if you're sending the quilt to a longarm quilter, is that the back is large enough, square and flat. I've done many, many quilts with pieced backs and several quilts that were actually two sided quilts. The quilt tops are centered on the quilt back.
Nan - Indiana