I've made a few quilts with flannel on the back. I've mostly used it on baby quilts, and only use it if I have the right color or width of flannel (I don't like piecing backs). It's so soothing when FMQ'ing with the flannel on the back - the flannel seems to muffle the usual clankity sound (maybe it's just my machine). But flannel is not my usual backing of choice.