Most companies find social media useful as a marketing and communications tool, but many companies also use social channels for sales, customer service, IT and more.
Although companies may use social media for several discrete business purposes, they should work toward integrating social media expertise into functional teams. Silos of expertise should be avoided.
I think the most important point is really, that Social Media initiatives are linked into the company and not a hobby of a Social Media enthusiast. Information needs to flow back and forth between Social Media, Sales, Marketing, HR and even executives.