I have and wear one of two. Depending on what I am doing. One for PGR missions and another for Southern Cruiser Rides. Good place to put sunglasses when not in use or gum just what ever small stuff you need to stash.
I wear a vest when it's not too hot because it is slimming.
The real reason is my holster clips to the inner pocket very nicely. Also it's where I have sewn my favorite patches.
Leather vest is convenient (plenty of inside and outside pocket storage), provides a bit of upper torso warmth and does have a certain amount of "cool" factor for pins and what not.
Actually, I wear an orange/reflective Icon mcycle vest b/c my wife wants me around for awhile (over my leather, of course). Guess a guy can never be too safe...:s