I was one of the "almost nobody" who has used it on my game

(
http://www.stencyl.com/game/play/4223).
This is disappointing news, as I think it was useful. You could use it for high scores, or use it to save player information so that it would be the same no matter which computer the player uses to play the game.
Kongregate is fine... if you use Kongregate. But also I don't think you can do quite as much with it besides a normal highscore list. Isn't it a bit early to decide when something is not useful, as many people are still new to the system and there really aren't that many high quality games out there made with Stencyl yet.
Of course the decision could be based on other factors not discussed here, etc. Oh well, I suppose high scores are not essential. Anyway, maybe when extensions are created someone can release a high-scores extension or something.