Depending on the nature and the size of the website. A sitemap is important to get all your web pages indexed, or at least found.
What is a Sitemap?
A Sitemap is nothing more than the list of all your active web pages.
Why use a Sitemap?
Easy, it allows the search engine spiders to index every web page that you want found. Also it allows your visitors to locate a web page quickly.
Be sure to have a link to your sitemap page from the main page. Then be sure to have a link to the sitemap on every web page.