I have never owned a truck without a flatbed (except a F150). I dont really like the aluminum ones as they fade (can acid wash them though) and dont seem to be as durable.
Some benefits are that you dont have to crawl over the bed sides to put stuff in, you can haul twice as much on the truck, and you can back 5th wheel trailers easier and sharper. No tail gate to worry about. Plus its made of steel you dont have to worry about tearing a nice bed up, if parts break, weld them back on.
Some cons, you have to strap everything down, not that big of a deal, some people dont like the looks, and your dog usually wont ride nice on a flatbed.
If your going to try and replace the flatbed, see how it is put on the truck, cause alot of people weld the bed onto the frame, so your in for alot of work to get it off to replace it with a normal bed. A proper mounted bed should use u-bolts, grade 8 bolts, and the 5th wheel plate to hold the bed on.
If you like the looks why not?