Slipping a 172 is only a problem if you have more than 20 degrees of flap (per the POH), and since I've always been taught not to put in more than 20 before turning final it's easy enough to put in a slip if you're too high in the turn. I don't much care for full flap on a 172 anyway because it likes to shake, rattle & roll when the flaps hit 30.