Having the PRUs as supporting microcontrollers can be great where timing is critical. For example, it's possible to decode signals from an AM receiver and pass them to the host, or monitor sensors and have immediate responses (such as triggering a shut-off via GPIO).
There's nothing particularly difficult about wiring a microcontroller up to a single board computer to do these jobs, I've done exactly that for reading my weather station and heating oil tank level. But it's messy and I think the cohesion of being able to do it directly on one board is a worthwhile advantage.
There's nothing particularly difficult about wiring a microcontroller up to a single board computer to do these jobs, I've done exactly that for reading my weather station and heating oil tank level. But it's messy and I think the cohesion of being able to do it directly on one board is a worthwhile advantage.