Once you have studied Category Theory, Maths, Prolog, Lisp, Scala and the like, Haskell seems to be another tool to spand your mind, but this time the language should be for communicating and expressing something more tangible. I am learning with Haskell and I don't know if I will find that key moments in which the language is able to express ideas or concepts that no other language is able to suggest. But there is always the risk of losing your way, forgetting that developing a product is the real target and dreaming of doing with a language that expand your mind.