Synchronous Core, Asynchronous Shell

I follow the same principle in my code, but doesn't the "functional core, imperative shell" pattern already push the async stuff out of the core?

What would be an example of an async operation that doesn't perform a side-effect (thereby needing a place in the imperative shell rather than the functional core)?

I think pushing async to the shell is really a subset of pushing imperative code to the shell.