From Elixir documentation:

Besides the modules and functions libraries provide as part of their public interface, libraries may also implement important functionality that is not part of their API. While these modules and functions can be accessed, they are meant to be internal to the library and thus should not have documentation for end users.

In the context of a Phoenix app where the end user is not necessarily an elixir developer, when does it make sense to use @moduledoc in the code?

I understand the need of using @moduledoc in the public API of an elixir project if it is a library to be used in other elixir projects. However, when the elixir project is an application (such as a web application), I do not see what modules should have @moduledoc.

Is there a good rule of tumb or guideline for when to use @moduledoc tags?