Right, though the former is just an exception. So what general effect systems provide above and beyond what we already have in most languages is "multiply-resumable" checked exceptions (also known as multi-shot continuations and often provided by "delimited continuations").

At the time I developed my Haskell effect system Bluefin there was a conventional wisdom that "you can't implement coroutines without delimited continuations". That's not true: you can implement coroutines simply as function calls, and that's what Bluefin does.

(The story is not quite as simple as that, because in order for coroutines to communicate you need to be able to pass control between threads with their own stack, but you still don't need multi-shot continuation.)