Not just rigor. Haskell is very difficult to debug performance issues of, and is hard to use when manage changing state.

Haskell shines when used to manage a sophisticated computation of a static result, not a constantly changing dataset.

Haskell is a great way to learn stateless pure programming style, since it forces a lot of discipline. Haskell makes you a better Java/Lisp/Python/C programmer. (Except that it will make you write inefficient Java if you get too accustomed to the idioms that are efficient Haskell)