A navigation is very convenient if the user is interesting in other stuff of your site after reading a page. From the SEO point of view, offering internal links pointing to other pages of your site benefits quite a lot.
make sure it's a usable navigation though. There are so many horrible websites out there where you get to a page and forget just how you got there.
In the WWW and information systems the process of goal-directed locating and traversing hyperlinked information, browsing. In simple terms, it means, going from one page to another or from one link to another by clicking on the anchor text. source : wiki
The site navigation is the links structure on your web pages and they will help people as well as the search engines finding and crawling your contents.