The sitemapxml plugin is used to generate a list of all the public pages in an XML file for robots to quickly know of all your website pages. This increases the likelihood that search engines indexes most of your public pages.
The system automatically breaks down the file in multiple files once you reach 50,001 pages. It also keeps the file compressed and thus serves them quickly.
The plugin supports a tag which one can add to a page to avoid having the page added to the sitemap. Private pages do not need to use that tag, obviously. In most cases, all pages can be added to your sitemap.xml files. Pages that are often removed are legal pages, site map like pages (list of links.)