The main reason to learn category theory for Haskell is to learn how much of the Haskell meme complex is wrong. Otherwise, it won't help the typical newcomer. I think it's important to explain that Hask isn't a category, that Haskell's type system is unsound, that Haskell doesn't have sum types, etc.

There are powerful applications of category theory to other parts of computer science. If one keeps in mind that Haskell is Just Another Programming Language, then one can apply category theory more generally and fully.