It doesn't take into account the whole range of errors that can creep into runtime. If a type system only moves 2% of programming errors to compile time, but co

It doesn't take into account the whole range of errors that can creep into runtime. If a type system only moves 2% of programming errors to compile time, but costs you in terms of coupling, complexity, and effort, it may not be worthwhile. This is especially true if you can catch that same two percent of errors with tests instead, and avoid the coupling and effort penalties. Personal opinion: Type systems are more useful for initial code comprehension and tooling than for writing it in the first place, or preventing bugs.