i'm waiting for a short cut through torghast...
Correct me if I'm mistaken, but don't you have to jump down from a pipe to get into that area where you can't get back up into the pipe again, with that being the only entrance/exit while the boss is still up? If so, that would mean that it's so people can exit the instance without being forced to use a teleport or dying. Useless? Probaby. But it ensures that you can exit the instance everywhere at any time. I think that's the reason it exists.
Neat little exit. That'll make the inevitable solo farming easier.