The two differences I can think of are 1. If you don't assume exception throwing (which may be valuable) then you can more easily distinguish

The two differences I can think of are 1. If you don't assume exception throwing (which may be valuable) then you can more easily distinguish one failure from the other. 2. It reflects in the type a more accurate representation of the effect going on. If such distinctions are undesirable it's a trivial `join` to eliminate them but if the distinction is never exposed then you can't get it back. So really, my thought is that given greater opportunity to distinguish between end-user meaningful effects it's worth exposing them by default. It should be a deliberate choice to hide them with join.