[nightcracker]

> And say there is absolutely no IO

Well, then we can simply optimize away your entire program as it does nothing and running it has no side effects.

Even if your program is entirely CPU bound, there are uses for writing in an async/await style. As an example, parsers can be quite natural to write in that style.

Or you can use it to have multiple computations running at the same time, and give updates on their progress. It is voluntary time slicing, which is significantly less overhead than the OS doing time slicing for you.