I used to use CoffeeScript because the syntax was more convenient. I could do the same thing with less code. Less code can mean less maintenance (although some people have said CoffeeScript can overdo this...)
Now I use TypeScript to get the benefit of type-checking. It really helps catch silly little mistakes.
I would use Civet just to be able to use the new pipe operator syntax.
There are even compilers that compile future versions of JS into the current version of JS so future language features can be used in current browsers.
What problem ist actually solved by being able to compile pseudo-languages like Coffeescript or Typescript into each other?