Not just shape of data, but the values that are allowed by data. I agree that it is an oversold fallacy and types get really clunky when pushed too far. But an

Not just shape of data, but the values that are allowed by data. I agree that it is an oversold fallacy and types get really clunky when pushed too far. But any worthy type system prevents lot of errors. This is not generally acclaimed by empirical studies claiming only 5% improvement because they are caught at compile time. Other benefits are enough to use a sufficiently good static type system, by the way, even for people that think type systems aren't better than TDD. * Better autocomplete * Better error highlighting - no need to run code or tests, IDE can highlight instantly. * No typos in variable names (can be achieved in some but not all dynamic languages) * Performance of compiled code