Aside from longarming, I think it depends a lot on the quilting. If you have a seam in the backing running the length of the quilt without quilting lines running over it periodically, then I would want a wider seam because of the additional stress the seam will be subjected to.
There really is no reason to use 1/4" seam on the backing anyway, unless possibly if you are handquilting (and even then it probably would make very little difference to a hand quilter).