USPS Shipment Confirmation Acceptance Notice (SCAN) for shipping labels
For bulk shipping of packages, USPS provides a service called Shipment Confirmation Acceptance Notice (SCAN), which allows people to print out a bar code to scan that will represent 10s of packages at a time.
WooCommerce Services plugin makes creating and buying USPS labels convenient, but it would be more convenient for those who have hundreds of orders a day to take these created labels and tracking numbers to reduce the time the post office takes to scan all the packages into the system.
You can find the API here:
This idea is similar to the one below but takes it further: