It is great for marketing your business, and depending on what business you have could also be used for direct sales. I get a lot of other benefits to it as well, especially from twitter. I've had a lot of people contact me there offering content for my website, and people who buy ads on my site always take my social following into account when deciding to book ad space. I also get a supplemental revenue stream from tweeting ads on my twitter account. I got about $500 (Izea's sponsoredtweets.com) doing that last year, which is nothing major, but it was basically free money so I'm not complaining.