If you are working in a team types are invaluable unless you have a very disciplined team.
The times I’ve worked on team JS or CoffeeScript code I’ve had to read hundreds of lines of code to understand wtf to pass into an argument. Aaah you want it to be a promise if the first arg is true but a number if it’s false kinda shit. Return type? Sometimes this sometimes that, might be a hydrated object from the wire as-is.