Why are monads important

Googling around for tutorials and explainers on monads you’re sure to find an embarrassment of riches. But, for a tutorial explanation that has connection with the OCalm community, and which I personally found very illuminating, I’d recommend the Std (monads.Monads.Std) tutorial (previously announced in the post [ANN] Monads - the missing monad transformers library).

A tl;dr of the point of view presented in that tutorial is: monads are important because they let you parameterize your computational model in a pretty elegant way.