If you are waiting for a hardware interrupt to happen based on something external happening, then you might use async. The benefit is primarily to do with code structure - you write your code such that the next thing to happen only happens when the interrupt has triggered, without having to manually poll completion.
You might have a mechanism for scheduling other stuff whilst waiting for the interrupt (like Tokio's runtime), but even that might be strictly serial.
You might have a mechanism for scheduling other stuff whilst waiting for the interrupt (like Tokio's runtime), but even that might be strictly serial.