This feature allows the request to be sent to recipients in a particular order, allowing you to create multi-level workflows.
Steps to set the receiving order:

If no receiving order is set, the add-on will send requests to all recipients at the same time.
A recipient set to level 2 will be notified after everyone at level 1 has responded.
This video tutorial (at 4m:07s) includes an example of setting the receiving order.