I think one of the major benefits of it is that you can send one courier with information about the passwords and money amounts, without having to send a wagon

I think one of the major benefits of it is that you can send one courier with information about the passwords and money amounts, without having to send a wagon or boat load of specie. That one person can travel much faster than a caravan and there is no risk of theft. A caravan takes large amounts of preparation and is a target for robbers.