Those of us who ride in an aero position (back almost flat horizontal) a lot will want these types of bars. Why?
1. when you're hunched down, the forwar sweep will give you extra room to stretch. Yes, extra room to stretch will lessen the strain on your elbows, and it'll allow you to breathe a bit better, and all this will mean you'll be able to hold that flat aero position longer (without using dedicated tri-bike aero bars)
2. then when you're sitting more upright, eg, you're climbing on the tops, or just chillin on your recovery ride, then you can sit upright without needing to stretch out.
I'm using a 120mm stem with a 50cm frame. And when I'm in my most aero position, I feel like I want a 130 stem, but I know that a 130 stem will probably throw the bike's handling a bit off, and a 130 will be a tad too long when I'm sitting more upright riding the tops. In my case, the forward-sweep bar makes a lot of sense.