The first cargo cycles or freight bicycles were used by tradesmen for delivering mail, bread and milk amongst other things.
The Post Office and Telecommunications companies were amongst some of the earliest to use these vehicles in their fleet.
In the Netherlands employees of cable companies used huge tandem cargo bikes as their work vehicles, lugging all their cables and equipment in the front. You can see more of them at Transportfiets.net.
Another common use for cargo bikes over the years has been vending. Here’s an example of a modern day ice-cream vendor using a bike as his store front. (Found on WorkManCycle.)
In modern times there has been a shift in the usage of these bikes, they began as utility vehicles, and while they still are used for this purpose it is just as common to see these bikes used for purely recreational reasons, like taking the kids for a ride or a picnic.
Over the years these kinds of bikes have been known by many names such as Cargo Cycles, Cargo Bikes, Freight Bicycles, Carrier Cycles, Freight Tricycles, Bakfietsen, and Porteur bicycles, to name a few.