A starting point in the search.
Not long ago people searched the web, found websites of businesses they were interested in dealing with, and then would purchase a product. That was yesterday.
Today people use the website to confirm that they are looking in the right place. Once they have found what they are looking for they begin to ask questions. You must be there to answer them.
With links to your Facebook or Twitter accounts on your website, you are inviting your prospect to ask questions. That gets you much closer to working with them.