[TheAsprngHacker]

I use OCaml, and monads also come up in OCaml code. Monads may not be as essential to understand in OCaml than in Haskell because OCaml doesn't use them to track IO in the type system, but people use them in OCaml to chain options and results. In fact, OCaml 4.08 introduced syntactic sugar that makes functor, applicative, monad usage more convenient. I'd say that monads are something that non-Haskell functional programmers should learn.

Monads also turn up with lists (flatmapping) and promises. Although you don't need to know what a monad is to flatmap a list or use promises, I'd say that being aware that lists have a monad instance or that promises have a monad instance provides insight.