What would happen if you used fleece for the middle instead of batting or flannel?

I make mine 3 layers, always flannel in the middle and then you can use any fabric for the rest. I do like flannel on the back to for my baby quilts. These still get heavy. My DIL was the one to tell me how wonderful they are, I just thought it was a cute pattern (4X7 with alternating rows of 4" on the ends) I recently received a thank you from my college roommate's daughter. She said it was her favorite gift and she was taking back the Pottery Barn quilt she received.