Sure, I can say more--put bluntly, and despite anything you might hear to the contrary, you basically do need to grok monads and monad transformers to tackle any nontrivial project in Haskell. Even if only to understand the code and APIs of libraries your application will interact with.

Basically, you can't swing a dead cat without hitting monads in the Haskell library ecosystem; therefore, you'll need to know what they are.