I've quilted from the back several times. Mainly because I was using a very matched thread to the quilt top (black on black) and couldn't see where I was going. My backing was a colorful print, so the black thread showed up very well. If you stitch in the ditch first (from the front), you'll be able to see where your blocks are and see the background area clearly, when on the back side. I've also done it when the front was pieced with many busy prints and it was hard to see where I was, where I was going, etc. The Quilt Police don't need to know and if they find out "So what?"