Stripping a website to its barest form, ignoring for a moment, content which is only text and images, all a browsing experience is, is navigation. It’s clicking links that take you to other pages with more links. The main navigation of your site is such a crucial part of this as it represents the persistent doorway to the most important pages of your content.
Many sites also have secondary navigation, relegated to the bottom of the site, containing ‘boring stuff’ such as Terms of Use, or Privacy Policy links; it makes sense not to have those links in your main navigation; you don’t want them spoiling your landing page. But here’s a hint, if you have to have a site map included in that secondary navigation bar, you’re doing it wrong.