XML Sitemaps are an imperative piece of effective SEO
Google will ignore links from web log sites and sites that are apparently setup only to link to other sites.
Google will return every page it has from your site within its index and will show you every page indexed under your domain name.
Google will index most of your website’s pages, except where you specify not to. Yahoo has indexed very few of your pages.
You can request Google to crawl your sitemap via Google Webmaster Tools
Google will do its thing and will use this sitemap for serving your content to relevant search queries. This enables Google to help users find whatever they need on your site.
Google will not penalize you for frequently updating your site map on Webmaster Tools.
Google changes their ranking alogrithms frequently, therefore it is important to keep yourself up to date with SEO in order to hang on to all of your hard work
The universal standard about sitemap.xml can be found on site sitemap.org.
When you add a sitemap.xml file to your root directory, the file points crawlers to all the pages on your website.
Other Helpful Items in Google Webmaster Tools:
Google Webmaster Tools can check your robots.txt file and help you correct any issues
Google Webmaster Tools can tell you if your website is too slow or quick enough.
XML Sitemaps are an imperative piece of effective SEO