What to do with leftover drywall?

I took my left over drywall and cut it into 12-15.5 inch sheets and glued it inside the wall (interior walls) between the studs I wanted to be more sound proof. I did it in the bathroom and my bedroom. Obviously you have to do it after one side is done and before you put the final sheets on the other side. You can do it to outside walls but you will limit insulation space and would have to glue it to the plywood or particle board.