You have to cast it every 5 seconds, that takes up too much time, especially when you're getting hit constantly.
You don't have to use it every 5 seconds.
What's the cast time on it? Anyone got a full skill description (I am not at the computer that has my elite skills page bookmarked )? Seems to me that it ends up being about the same as the other energy gain spells if you use it once every 10 seconds....but it also could refresh you energy quickly when you have a few moments of down time.
If the casting time is >1 second, then I would have to agree that it's not helpful. *shrug* Maybe I'll just have to find it and try it to really see, but just because something has a recast of 5 seconds doesn't mean you have to spam it to get maximum efficiency...