From Kin Lane, more useful information for why it's important to own and control the content I create on the web:
While I have my online brand to protect, and overall I have a heightened awareness around my online persona, this is something everyone should learn about. You may not have a valuable blog, online portfolio or other valuable online assets, but eventually you might. No matter who you are online, you should work to understand where your content, images, video and other assets you generate reside, and retain as much control over them as possible.
The business model of major companies like Twitter, Facebook, LinkedIn, Flickr, Instagram and Youtube are all based upon you generating valuable content that people want to view, which then allows these companies to generate revenue by selling advertising or access to your (their) content. It is in their best interest to retain as much control over your content as they can.