Your glide will improve, but you will get a significant change in trim and nose attitude (you'll have to keep the nose higher to maintain the speed). It's easy to lose significant height doing it, so make sure you have enough!
Some interesting discussion on 'slipping cessnas' thread re. accurate approaches and flap.
Just saw XXX's pictures, certainly don't 'dump flap on final', but easing some flap off early in the approach will have the desired effect