When working with Managed Navigation, menu items linked to pages with specific permissions set are automatically hidden from users without those permissions.
When building public-facing websites often there are sections of the website available to authenticated users or users who have specific permissions, such as content managers. Usually you don’t want to display those links to everyone, since clicking on such link would display an error.
When using the Managed Navigation and modeling the site navigation with Terms, as long as the particular Navigation Term is linked to a page using the Term-Drive Page with Friendly URL option, the term will be displayed to users only if they have the necessary permissions to access the associated page. If you use the Simple Link options instead, the link will be always visible despite what permissions the current user has.