A sitemap is a simple file which contains the URLs of all the pages on your website. It is recommended to submit your site's sitemap to all search engines as it used by search engine bots to crawl your website and traverse all the links.
If you do not submit a sitemap, then there is a possibility that some of your webpages may not get traversed by serch engine at all. This is because search engine bots reach a web page only through a link and if they don't find a link to the web page, it may never get read by them! [More]