One of the key tenets of SEO is to not let your content become stale, and this means refreshing your content every couple of months or adding new content. New content gives search engine robots new information to index and indicates that your website is constantly evolving and developing new and organic content.
Content is also rated by its freshness (the date of inception), the older the content the less fresh it will be and the less value a search engine will attach to it. New content is important for the following reasons:
By refreshing your content, search engines will return to your site and crawl it again. This means that pages that were not crawled before stand a higher chance of being crawled. These updates should happen on a regular and consistent basis in order to teach the robots that your content is constantly updated, and ensure that they return to your website regularly.