In my case, you can set you forum subscriptions to turn on to every topic you reply to, meaning if I post in a thread, I'll get a copy and a link to every reply in that thread. Its very handy to stay up to date since I can read them from my e-mail.
I try to remove subscriptions when I remember, I can recall having to unsubscribe from forty something threads.
I approve of this move to de-congest the e-mail server.