The real benefit I'd be looking for is the chance to give the compiler hints to speed up execution times.
I personally find that type safety cuts down the number of unit tests I write by half and makes refactoring work an order of magnitude easier to perform.
While this is true, static type checks do even less for this problem. Do you even create specific types for value ranges eg IntegerBetweenZeroAnd100? You're in a vast minority if so, and I'd be interested to see how tedious it is to construct all these non-native types everywhere.
> If you omit manual type checking in your code or in the respective unit test, you may miss some subtle failure scenarios.
There's generally not much that's subtle about a wrong type. If the code is executed at all, it will usually blow up. In my experience, the subtlety comes in the values.
> I personally find that type safety cuts down the number of unit tests I write by half
I just don't buy this (but then again my team goes for near total coverage). Nowhere near 50% of our tests are testing anything that would be solved by static types.
If you're going to make the argument that you can just add comments with the types - well then that's exactly what mypy is doing, but if you do it in the mypy format you get static analysis of your types for free.
Static typing and unit testing aren't mutually exclusive.