After maintaining a huge JS codebase for years and finally upgrading it to TS, my life is so much easier. Refactoring is faster and less error-prone. I no longer have to manually document the parameter/return types for every function. I don’t have that gnawing “oh damn, what if I missed something” feeling whenever I make changes.

Yes it’s a bit more work up front but it pays dividends on larger codebases.