I was recently looking at the courier's parcel tracking app, i was interested recently to see that my delivery was '120 stops away'. If this is typical, the marginal cost of delivering a parcel must be small in terms of miles driven and driver time. (Obviously this is highly contingent on population density).
Another good example of this is Royal Mail, where the cost of a marginal piece of post or small parcel must be tiny (since the postman is already delivering to 50%+ addresses every day).
It occurred to me that in some situations, it might actually be more efficient _not_ to batch. The complexity of attempting to batch at the warehouse must be very high, and take up quite a bit of warehouse space, and slow down dispatch significantly.
A related and relevant observations why are courier companies not a natural monopoly? If the marginal cost of delivery were high, a courier company with higher volumes would naturally make more profit, and so the market would push in the direction of fewer bigger couriers. This seems to suggest that the volume of parcels means that we're already in a situation where couriers are pretty efficient and marginal costs are low. It'd be interesting to know empirically how this works out.