A programmer will still need to write correct code, but in your first example the error happens at the boundary between two modules. In the second example, the

A programmer will still need to write correct code, but in your first example the error happens at the boundary between two modules. In the second example, the error is fully contained within one module. One of those two is easier to spot, either by the original programmer, or by a code reviewer, or by someone trying to track down a fault. If all the type system does is make semantic errors easier to spot and fix, it's still offering a lot of value.