I'm not totally sure about here, as I have all notifications turned off, so not sure if it notifies you if someone you're following has posted an image or media, etc.
I do know, that if you follow members of the forum here, in addition to seeing them listed in the Members Online box, it will show their avatar above the text list. That way you can see immediately who you're following is online when you are, which is quicker than having to scan the text list, as that can be busy depending on the day, and/or time of day. Then you can scan the New Posts listing on the main forum page to see if they've posted anything new, or scan the New Resources to see if they've posted anything there, since last time you were here.
Needless to say, this is fairly new software compared to tried and true forum software packages most forums use, so there may be other ways the "following" of other members can be beneficial. I'm just not sure what they are.