Yes, if your app is a high performance server app, measure in that environment.

But user-facing apps (the sort people run on laptops, say) have async I/O as table stakes, really. It's not even about throughput or CPU cycles: it's about the fact that if you have I/O latency on any thread the user interacts with the user experience will be terrible.

Now in practice maybe that means "just make the I/O async, but the performance details of that don't really matter too much".

Anyway, the overall comment was about performance profiling in general, not just async I/O.