On the contrary, the significance has everything to do with the category-theoretical pattern, albeit the reasoning for that is not immediately obvious and has to do with a further category-theoretical tool known as the Kleisli category. A monad with no enforced "outside" structure is known as a free monad, and is basically the equivalent of what most people outside FP call the Command pattern (or rather, a well-behaved version thereof). And "Commands" have everything to do with specifying side effects!