I’m currently using mix xref callers MyApp.Schema – a module namespace that contains all my DB (Ecto) code. I’m integrating it in a GIT pre-commit hook that checks which modules use that namespace because I only want certain modules to directly use DB code.

So that’s one valid usage: you can enforce some limitations on your project at GIT pre-commit or CI server level. You can call it homemade linting.

Another very good usage is refactoring. When you move functions around – or rename them, or delete them – you want to minimise compilation or runtime errors so you first search who calls them and rework those as well along the way.

I was using mix xref within CI.

In detail:

• mix xref unreachable --abort-if-any
• mix xref deprecated --abort-if-any

But as with Elixir v1.10 these checks will move into the compiler.
I will use instead:

• mix compile --warnings-as-errors

Do you use mix test --stale? If yes, you are using mix xref more than you might know that you use it.

Similar if you use the ElixirLS. It builds upon xrefs result asas well.