The site map is a hierarchical representation of your website at a unique page, usually at a location like "yourwebsite.com/sitemap". The layout and design of your site map is something generally left up to your designer/developer, but in Sitemason, you are given control over which pages are displayed or omitted from view.
In a page's Settings, there's a single checkbox for "Include in Site Map". When selected, the page will display in your site map along with all other pages. When unchecked, the page's link will be omitted from the site map. This does not mean the page is inaccessible. It can still be pulled up at the given path, but it will not be listed in your Site Map.
This might be helpful for content that is currently being drafted or edited, a page that isn't necessarily private, but doesn't need to be accessed by average users, or perhaps an effort to simplify the Site Map of a large website.