You can cast farther with a longer rod. You also move more line on the hook set. Another bonus is that a longer rod gives the fish more leverage, so you get a better fight with the longer rod. Also, I prefer a fixed float to a slip float, and I can set my fixed float rigs at 9 or 10' deep and cast them easily with my 12' rods.
I use short rods in certain situations but, for playing fish, I'd choose my 12-footers every time. Seven to eight foot rods are great for casting jigs.