Another great use scenario would be for game devs that want to make extremely robust hand animations.
Depending on where you get them from, sometimes mocap data doesn't include data for hands and fingers, which is where the double leap motion setup would incredibly useful.
Say you want to use a leap motion to make a knife wielding animation, but if you only have a single leap motion, a good portion of the hand could be hidden from the single Leaps FOV, but if you have two, or more, it could simply use the composite the information caught from another angle, so you still get the entire hand's motion, without the knife, or gun, or whatever item.