Google introduced Google Sitemaps so web developers can publish lists of links from across their sites. The basic premise is that some sites have a large number of dynamic pages that are only available through the use of forms and user entries. The sitemap files can then be used to indicate to a web crawler how such pages can be found.Google, MSN and Yahoo now jointly support the Sitemaps protocol.

For an example, is a forum using dynamic pages. Google would only return less than 100 result without using sitemap. Once sitemap is provided, there are more than one millions pages result. Since MSN, Yahoo, and Google use the same protocol now, having a sitemap would let the three biggest search engines have the updated pages information