for me....and I am only talking about my piecing and quilting.....there is such a difference in the way batiks and quilting cottons "behave" while piecing that I prefer either all batiks or no batiks..... have to admit I feel the same way about mixing flannel in with quilting cottons while piecing.......as for use as the backing fabric - that has never been any problem. just my experience tossed into the mix here.