JFBConnect can autopost content when it's created to Facebook, Twitter and LinkedIn; it can help you manage your Open Graph and Twitter Card tags and it can add the social buttons. That's in addition to the other JFBConnect features, like authentication and profile import.
Yes, plenty of other extensions have some amount of social integration. The benefits of JFBConnect are a single, constant way of managing social networks on your site. You can choose to use JFBConnect solely, other extensions, or a combination to suite your needs.
Thanks,
Alex