Coming in faster gives you more rudder authority and increases the buffer in case of wind shear. With full flap on a normal approach you are wallowing around with less responsive controls, but if you were to come in faster with full flap you will float. Come in faster with less flap and you'll stop flying sooner though will have a faster touchdown speed.....
Isn't 80kts in a PA28 a bit fast for final and full flap?....I'd have thought than 65-70 kts would be better (it has been a while since I have flown a PA28 though, but it still seems quick).