Thanks to everyone on this thread for posting your experiences with pieced backings. I am more or less following a pattern for a baby quilt and bought the recommended yardage for a backing and it is just barely enough using a diagonal seam (I need 2.98 yards and bought 3). And I’ve never done the diagonal seam backing before, so was considering adding piecing.
But I soldiered through the diagonal seam with great success. I was even able to match the pattern in my fabric, which was shocking given, again, I had no extra. Photo of my diagonal seam attached.
For me, a pieced backing will have to wait for another quilt.