I realize that a very quick "who cares" may be in order. Here is a sentence and a brief, popular level article on why it might matter to learn more about social networks, why doing research on such things can actually make a difference, and where it might apply.
Communities Aren't Just Places, They're Social Networks - by Richard Florida in The Atlantic Cities
You don't have to be a Richard Florida fan to appreciate the somewhat obvious sense that communities are about people. Just consider what we'd have in our cities if none of us were around.