Search Engines like to include web pages in their query results that provide plenty of relevant content, either directly or through introduction and linking to other pages. It is hard to argue against the consensus that "content is king." Thus, when people attempt to improve the chances of ranking through the process of search engine optimization, content is a priority. Through research and testing, many SEO's have found that keeping content "fresh" is a way to gain the favor of the search engine spider, especially if the content is expected to change. That is - if your content rarely changes and the content of what you would consider to be competitor websites does, chances are that you will not be able to keep up when competing for highly popular keywords.
An interesting thread started a couple of weeks ago at High Rankings Forums has a member asking which is better for the overall SEO efforts of a website: simply updating current content or adding fresh content to the web site completely new pages? Some good points made so far in the debate include Chip Johns'
Remember, there are no definitive answers when it comes to SEO. If you have a site that deals with medieval history, many of your pages are not going to change, because, for the most part, history doesn't change. Google may prefer that pages NOT change in this instance.High Rankings Moderator Torka also adds an interesting thought:
When you make significant changes to the content of a page, there can be (at least temporary) rankings drops as the SEs sort out where the new page should rank.
Content will always be important to a website. Although the above example shows a possible topic that could be considered "safe" if it remains unchanged; I feel that the linking and some of the commentary probably should change, in order to keep up with recent research and discoveries dealing with medieval history.
Please comment on this topic at High Rankings Forums. It would be interesting to hear from people who have experimented with both content-freshening techniques.