I have quilted 2 sided quilts on both my domestic machine and my longarm.
Sometimes if you hit where two seams meet on both sides you have a problem, like in a center of a 4 patch, but I just try to avoid the centers in choosing a quilting pattern.
It defiantly helps to have a quilt on the bottom that is not as detailed. I have so many quilts to finish and so little time it helps me get more done.
But not all quilts are a candidate for that type of quilting. I would never attempt a Bonnie Hunter mystery quilt with all those pieces as a good choice. Having said that I have used "scrap" and "string" quilts as backs. I also often take my leftover pieces of fabric and sew them together in rectangles and strips and squares to make a pieced back.
If you quilt by checkbook, check with your longarm quilter because I have two friends who quilt for other people. One will do double sided quilts, the other will not.