As any informed blogger or SEO guru will tell you, having unique content on your website is more than just a little important these days. Ensuring Google (and other search engines, lest we forget) see you as a credible and unique source of information for the content you write is one of the last things on the web worth really protecting. After spending quality time writing and optimising your content it gives you the wookies if people steal it.

NB: There are a lot of ways people can get your content and use it for evil. One is the simple copy and paste. Two is using a scrapper to 'scrape' your information from your site automagically. Three is taking RSS feeds and importing them as posts on their own sites without including a link to original. And there are a few more no doubt.