Today there are a lot of services on the internet that are designed to follow every step we take and document it in databases for companies to make money with. Google's add-sense is an example. They can track you on every website that uses it and that's a lot. I supspect it works the same way with facebook, twitter and G+ buttons. And this is just what happens if you are not even participating in any of these networks. That's the reason I prefer if it's completely removed from my build rather than just disabled. If it's not very well implemented, "disabled" could mean that the buttons are just invisible but everything else still works. Also I like software that is modular and has some optinal parts that can be disabled. Some other arguments against this feature have been identified earlier in this thread.