Back in the day when I was doing theatrical costuming, I often used the back of the fabric because it had a nicer texture than the front. When I am piecing a quilt now, I look at the fronts and backs of my fabric to see which one gives the effect that I am seeking. I think that in the present almost anything goes with quilting. We are not limited to just 100% cotton fabrics, so why limit yourself to using only the front?