Starching the backing will help eliminate puckers when you sandwich the quilt. I've tried it and it does work well. Once the quilt is sandwiched and pinned/basted, the starch won't give you any issues while fmq. I believe that as you puddle up the quilt in the harp of the machine, the starch flakes off - just like freshly starched clothes (the starch is nowhere to be found after a couple hours of wear).