At the moment, "Following a Topic" does two things, that I can ascertain:
1) It places it in a list which you can see in your "Control Center" for management
2) It allows you to receive an e-mail every time there is a change to the topic.
I don't think #2 is applicable, so I may remove that option completely - I don't know of any reason why people would want *more* email from a system like this.
You don't have to be "Following a Topic" to see what Topics and Forums have new messages. This comes for free when you are a registered user.
It may be that the list which is maintained (#1 above) will be where I tack on "Check Subscriptions" support, but I won't be looking at that project for a bit now.