Well, if you are anything like most website owners out there, it's probably been several months or even years since you really made a significant change to your site. In order for a website to work to its full potential it needs to be cared for by regularly adding and updating content.
Keeping your website fresh accomplishes several goals. The obvious reason one is that it gives your visitors a reason to come back to your site often. Another benefit to updating your website frequently is that it could help increase your search engine ranking. Search engines like to come back to your site and see more and more keyword rich content every time they visit and will reward you accordingly.