Like having a subion page for each user for every thread they subscribe to. It's definitely useful for people who are Roleplaying or have a certain topic they would like to follow. Instead of constantly lurking on a thread for a reply. xD

Plus I bet it would save a whole lot of time than to just sit there and refresh a bunch of times until there's a reply. It would be more convenient than having pop-ups as well.

Edit: Also, sorry if someone already posted about this. D: