Every project I've converted from JS to TS, no matter the size, even the small, only a few hundred LOC projects, has had at least one major "how the hell did this ever work" type bug that the type checking discovered immediately and would have prevented from happening in the first place.

So I don't really do even small projects without TS anymore. Anything more than can fit in my text editor, without scrolling, with the editor window tiled so I can see the app and the debug log at the same time.