Some couriers (DPD? UPS?) in the UK take this a step further and will even come with the label ready to stick on the box.

Great if you don't have access to a printer.

I recall (perhaps incorrectly) that Royal Mail once offered a service where you could buy an "online stamp", then you would write a long string of letters and numbers above the address on the envelope to send it. It was distinct from freepost.