Imagine bypassing the national postal system or big-multinational express shipping companies and using other individuals as kooriers (couriers): regular folks delivering for each other for a fee. No more waiting in long lines, no more filling out cumbersome shipping and Customs forms, and even no more packing with boxes, popcorn, bubble wrap, tape, and shipping labels.
The extra, unused space in a travelers luggage or vehicle is prime real estate that can be rented out for extra income. If you are driving from San Francisco to Los Angeles, or flying from Dallas to New York, or London to Beijing you can deliver for someone else for a fee.