I am sure that if you search about what you should include in a social media policy or its benefits you will find a lot of results on any search engine. The policy become necessary when your employee have social interaction over internet with a lot of people all over the world and you don’t want for this to interfere with your business. There are a lot of cases in the last few years about people losing their jobs because they have commented onTwitter or Facebook or they have posted on their personal blogs about their experience in your company or about their opinions about your clients.
Don’t be very restrictive
You can not forbidd people to enjoy themselves and use social newtork. Also, don’t creat a list with do not share things: it will only be longer and longer with time. It’s better if use the policy to set some guidelines instead of do not dothings.