Every business needs a social presence nowadays. Besides providing companies with an excellent platform to reach out to and engage with their customer base, having a strong presence on social networks like Facebook also helps increase search engine visibiltiy.
16 million local business pages have been created as of May 2013, this is a 100% increase from June 2012. If anything this proves that your small business should definitely have a presence on Facebook. However, the questions of how much time you devote to it and how you use it effectively are very different matters.