Types help you prevent errors while writing the code instead of while running. That's a massive benefit, as it literally makes a lot of errors impossible (as long as you don't work around it) - otherwise you have to write a lot of tests to get the same guarantees, and you could always miss something by doing that.

The other benefit is that it allows other developers to understand your code very, very quickly. Types describe what your data looks like - there is nothing more important in programming than that!

When you install an NPM library and your editor gives you hints about parameter types, return types etc., that's all Typescript types at work.