I've only used TS on the frontend, but I had the same opinion as you until I dug into a couple of TS projects. I don't know if I've ever caused a JS production bug that was a type error at its core, but I've had plenty of bugs like that in development. TS lets me cut out those little dev cycles where I'll write some code, rebuild the app, then see an obvious error in the JS console when I run the app. That adds up to a lot of wasted time over a week of coding. Smart autocomplete and smart variable renaming is also really nice, and I have way more confidence refactoring a TS project than a JS one. I think using TS does result in fewer production bugs, but the big win for me has been having fewer development bugs.