Certainly, not all tabs in the project menu are provided by modules. Thus, even if all project modules are disabled for the project, it will still have the three core tabs—Overview, Activity, and Settings.
The Overview and Activity tabs are public and the Settings tab is visible only to project managers. We will talk about the Settings tab in The project configuration section. Right now, let's speak about the first two tabs.
The overview page is the landing page for the project. That's why it combines all of the information that can be of interest to users. However, it needs to be stated that users who use Redmine intensively rarely come to this page, as they know where they can find the information they need. On the other hand, new users of the project, especially first-time users, come to this page more often. So, it can be concluded that the overview page is intended mostly for new users. Still, this page contains some information that you won't find elsewhere...