AFAIK Elm doesn’t perform runtime checks, does it? One benefit of types is auto-complete, of course. The other benefit is that knowing the type of your input you can successfully guide it through your system to an expected output. That’s how all statically typed languages work: they don’t have runtime checks. It’s not for nothing that teams switching to TypeScript see a decrease in runtime exceptions (speaking from experience). Our bug tracker was reduced by more than 80% after we finally completed the switch from JavaScript to TypeScript.