Doug,
The first and obvious advantage is clean up. I can go multiple smokes without changing out bottom or smoke box foil. I use it for butts, briskets, turkeys, just about everything but ribs.
A couple of weeks ago, when I made my turkey, I added a couple of cups of water to the pan initially and had enough broth and drippings afterwards to make some great smoked gravy. On other cuts of meat the dripping captured in the pan with some broth makes great Au Jus to moisten the meat after it is carved.
I usually have my meat rack 6" - 8" from the top of the smoker and the drip pan another 6" under the meat rack.