When you follow someone you will receive a notification anytime they create new content. Such as a blog or forum topic (or articles if they can post those). You won't see replies to topics created by other members or anything else.
You may also see when they create a Daily tourney but I'm not 100% positive on that.
Sorry if this is an obvious question, but what does following someone actually mean?
If someone doesn't write any blogs is there any reason to do it? Do they know when that person is on-line, for instance?