I went to a strength and conditioning clinic at which Anthony Clark demonstrated his bench and told us about the grip and whatnot. Here's the reasons that he gave us for using it.
1) I believe he said something about getting injured and then needing to come back. Well, since he, at the time, was the only person using the reverse grip, it gave him a certain PR advantage.
2) With the reverse grip there is only two rotations in the shoulders as opposed to three with the conventional grip. This takes a lot of stress off of the rotator cuff and helps prevent injury. Also, I think the injury he had was to his rotator cuff, thus using this grip is definitely better for him.
Personally, I can't lift as much with the reverse grip, due to lack of specific practice, but I like to use it every few weeks or so because I really get a good workout in the medial heads of my delts. Don't know why, but I do, so I use it here and again.