HTML site map can provide value for many things and help you in many different ways. Html sitemap will help a lot of SEO, google bots come to know about your deep link topic .
You can use your atom.xml feed and submit it to Google's sitemap
Yes HTML site map is necessary for a website.It helps the visitor to find your webpages easily. :)
Html sitemap will helpful to users to find all pages from one page.This site map will give you the full preview of your website.
Sitemaps are often a great way to improve search engine visibility because it enables all pages to be found. With many websites, for example, the navigation is in flash or some other technology, such as AJAX, which makes it difficult or impossible to be crawled via search engines. Sitemaps correct this problem. Additionally, sitemaps are particularly useful for large websites, frequently updated websites, and websites full of archival content, whose pages are hard to reach via links.
Yes this may help users really want to know something about your website
A few comments:
1.) Even if you're using AJAX, if you're doing it right, your site should still be crawlable by bots.
2.) If you're doing your main navigation correctly, there is no need for a user html sitemap... if a user needs to reference an html sitemap to navigate your site, your navigation is broken (that includes indirect methods like site searches).
3.) You definitely should do an xml sitemap. When bots crawl your site they crawl at the hierarchy given, if certain pages are too deep in that hierarchy they may be missed due to bots limiting both the crawl time and depth. Providing a sitemap essentially gives the bot a flat view of every page of your site all in a single location, which means it can crawl those often missed but possibly useful pages.
Using sitemaps has many benefits, not only easier navigation and better visibility by search engines. Sitemaps offer the opportunity to inform search engines immediately about any changes on your site. Of course, you cannot expect that search engines will rush right away to index your changed pages but certainly the changes will be indexed faster, compared to when you don't have a sitemap.
It is the xml sitemap that search engines use. Unless you have an exceptionally large site I don't think an HTML sitemap is necessary if you have clear navigation on your pages already.