I believe that it isn't necessary to point out the benefits of having a sitemap somewhere on your site. Apart from making sure that all of your pages are linked and indexed, you are providing an overview of your site's structure. That can be very useful to some user trying to find his way around. But, what happens if you have huge sitemap and you don't want to overload your page yet still keep things accessible and "indexable"? Maybe CSSG Sitemap Styler could help.