Should I add a Site Map to my website?

Hi Ngoc Le.,
Normally we have 2 kind of sitemap: 1 HTML sitemap, this one mostly for Users ( visitors ) and secondly we have the xml sitemap, this one for Search Engine like Google, Yahoo, Bing...
As a HTML sitemap, sitemap just like a map in a big palace, your visitor wont get lost of your site if you run a big site. More over If you connect your important pages in your site map users can navigate easily to any page listed in the sitemap and return to the main page without loosing their path.
As a XML sitemap: Using sitemap is very importance for a website, it's not only easier navigation and better visibility by search engines. Sitemap offer the opportunity to inform search engines and get them index your site faster about any changes on your site.
So I recommend that any website should have a sitemap, it's good for your users and for the search engine to crawl your site faster.