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Yep, they're a communication and documentation tool that happens to have pretty-good machine readability and correctness-checkability. Sometimes the person you're communicating with is your future self, is all. Sometimes it's just yourself five minutes from now, even.

They didn't mention big codebases or working on a team, though. Also, you can just use JSDoc.

Even in a solo project, you import libs from others. Never felt the need for those libs to have types.

Every use case is different.