"enforce the verifications across the code" is the point.

I've worked with a ton of Python code that looks like this:

    def foo(bar):
        # do stuff
        return baz(bar)

What does `foo()` return? I have to go read the body (or docstring if I'm lucky) of `baz()` to know that. And `baz()` might be another level of indirection to `quux()`. If I change what `baz()` returns, now I need to grep my codebase for all call sites of `baz()` and verify that the new return type is acceptable at each of them, and make changes if not. This is super time-consuming and error-prone, especially when a compiler (especially with an IDE refactoring tool) could do take care of it for me in seconds. It's easier if I have a good test suite, but that means I'm just implementing static type checking with runtime tests, which is more code that I have to maintain.