It lets people share a thread on Twitter, Facebook, Google+, EMail, etc; free advertising basically. Ultimately it's what I envisioned the Facebook/Twitter "like" buttons that we've had in 7.5 being when I approached Rick about it several years ago.
When a user "shares" the link (just by clicking the button) it shares it on the social networking site and adds +1 to the tally on the counter for each service (I clicked the Facebook one, see how it shows a number next to it? If you click it then it'll increase accordingly).
How does it work, well, you slap their code into your forum as per the directions above; how does it work on their end, I have no clue.
