Need of Sitemap

A sitemap is a great way to show the search engines the structure and organization of a web site. This helps the search engines find pages that may have not been properly linked throughout the rest of the site.
In its Webmaster Guidelines, Google touts the merits of adding a sitemap to your site.
” We don’t guarantee that we’ll crawl or index all of your URLs. However, we use the data in your Sitemap to learn about your site’s structure, which will allow us to improve our crawler schedule and do a better job crawling your site in the future. In most cases, webmasters will benefit from Sitemap submission, and in no case will you be penalized for it. ”
I have to say that I recently saw a new site where it was sandboxed. One week after adding the sitemap there was a couple thousand percent incerase in the pages indexed.
As a Webmaster, one of the things you always need to be aware of is how well your the pages of your site are interlinked. To combat this, you can generate either an XHTML or html Sitemap that contains links to every page of your site.A properly constructed XHTML or html sitemap solves this problem