What I really like about notifications is that it no longer requires a topic to be on "page one" to be relevant. I could reply to a member days later (when I come across their comment or reply and feel an urge to respond), I post something, they get a notification and the conversation is dependent on people talking, not people bumping or making noise. I could follow someone I never knew about, page through a bit of their history and find something to talk about, even if it was days/weeks old. No accusations of necro-posting, no worries that "well this got stale fast", the content of the conversation is what keeps each conversation going. Plus, it is nice to see that people have responded to you too.