If you are writing code by yourself and your code base is relatively small, then I agree it's hard to see the benefits at first.

If your team and code base grows, one of the first things you'll notice is a lot of time wasted trying to figure out what parameter types a method takes. If you can imagine, a new person onboarding on your code base and having to figure this out constantly and then forgetting, is pretty inefficient.

TypeScript solves that problem since you declare types explicitly in code. The new person will know exactly the parameter types, the IDE can support you more intelligently, and you'll get upfront compile time errors.

The downside is the initial setup and the extra effort of declaring types, so it comes with a cost, but personally I think the benefit outweighs the cost.