> Generally though, while I think the passing around of state through effects can be useful it isn't the most convincing use of effects.

I actually find it quite convincing, even if it might not be the main use case. Nowadays in imperative languages there are countless popular frameworks that resort to using & manipulating global state behind the scenes because drilling context through the call stack by hand is painful. Unfortunately, this makes understanding code much more difficult and testing it even more so.