I believe it’s more about robustness than performance in typical cases. Without pre-emption, there’s always a risk of one goroutine using disproportionate CPU time if it gets into an infinite (or just very long) loop without doing any IO.

You can try this yourself: GODEBUG=asyncpreemptoff=1

Also platforms like Wasm still do Mx1 scheduling without async preemption, where Gosched is required at places.

E.g.: my "transpiled" SQLite driver takes special care to make sure long running SQL queries (and the busy handler) can be canceled with contexts even on platforms without async preemption.