Ah. So what isn't Haskell good for?
When one is fluent in Haskell I think the language naturally tends to drive you towards well-factored, reusable designs that can handle change well. I say "fluent" because I don't think one needs to be "expert" to get to this level, but certainly there's a level of experience required to be here. Beginners and pre-fluency intermediates in the language produce god-awful messes of code. (I know, because I have! Fortunately I had the foresight to do that to throwaway personal projects, rather than critical business projects.) I think a great deal of the Haskell propaganda is justified, but beware the Haskell enthusiast who recites the propaganda, but can't clearly explain in their own words the mechanisms that Haskell uses to accomplish it.
Actually, scratch Haskell out of that. Beware any tech enthusiast who can't give a coherent explanation in their own words of why the tech stack has the claimed effects, but just repeats the propaganda again.
First, is it Haskell that drives you toward well-factored, reusable designs? Or is it functional programming? (I know, you can't do Haskell without functional programming. You can do functional programming without Haskell, though. Can you separate the two, and say which one is driving you here?)
Second, have you ever seen Haskell deployed in a large, long-lived production code base? How large? How long-lived? How did it work? (I ask because I remember reading an article on Lisp, which said that X in Lisp is just like Y in an object-oriented language, "with the proviso that in Lisp, all the types exist in the programmer's head". I'm pretty sure that won't work very well on a million-line code base that lives for 30 years. Haskell has a very solid type system, so it won't run into that particular problem but... does it have a track record for large-scale work out in the real world?)
In my opinion, it's the purity, and the general simplicity of the individual pieces which forces you in certain directions. Since this conversation is dead-ish now, it's probably not a big deal to link to my longer musing on this: http://www.jerf.org/iri/post/2908 Even functional languages that make impurity easy and available end up making it too easy to jump down the escape hatch.
"Second, have you ever seen Haskell deployed in a large, long-lived production code base?"
I personally have not. As I said, where I work I tend to tamp down on any efforts to use Haskell, and there's not many! But I trust the people who have and do, and who knows, perhaps may join them someday.