Caching a page can dramatically increase the performance of a Web application. However, in some cases you need most of the page to be cached and some fragments within the page to be dynamic. For example, if you create a page of news stories that is entirely static for set periods of time, you can set the entire page to be cached. If you wanted to include a rotating ad banner that changed on every page request, then the part of the page containing the advertisement needs to be dynamic.
