the publish interface is used to decide if something is "published". its a rather abstract concept, but the current implementation uses the start and end date plus a boolean flag (that was added recently and is not explained here yet at all). but then depending on your role you might still want to see that content.
in the menu for example, unpublished things are silently removed. if a mainContent is not published and you do not have the configured role, you get a 403 page.