They are useful for catching issue before code is committed or deployed. At my work we run mypy as part of our test suite, so failing type checks will block a merge or deploy.
How will they catch issues if they are not checked? The comment I'm replying to insinuated type hinting is just for documentation, and not necessarily meant to be actually checked by the tooling.
You seem to be describing actual type checking, which I understand (though in my opinion, mypy is not a satisfying tool for this).
