But they are a good thing, from a type perspective, they encode the idea that a side-effect is going to happen at the type level, and then force you as the call

But they are a good thing, from a type perspective, they encode the idea that a side-effect is going to happen at the type level, and then force you as the caller to handle that fact or pass the buck to your caller. Effect types are a signal for all programmers that "Here be dragons". They outline parts of your code which may not be safe to reorder during refactoring. And they can cover so much more than just asynchronous I/O. [1] 1. https://en.wikipedia.org/wiki/Effect_system https://en.wikipedia.org/wiki/Effect_system