The aggregate peak backplane utilization is all of the device’s interfaces transmit and receive put together. This allows you to see when the device is working harder at different times of the day. It also allows you to understand when it might be a good time for maintenance/shut down of that device because you can see when it’s the most quiet.

Also: If you see a spike of utilization there, you can then go into each interface and find the two interfaces involved in the spike.