I'm not an expert. My tractor mechanic was working on my swather. I asked him why the diesel engine ran so well. I drove it out to the field and it zipped right along at 6 or 7 miles an hour. Once I started cutting hay it just bogged down and had no power and the engine died. He said an idling diesel requires almost no fuel to keep it running. Once you apply the load it then starts to consume the fuel. Very little expense letting a diesel run Vs turning it off and back on and warming it back up again. The diesel probably takes more fuel starting it and warming it up than idling while making deliveries. If that delivery man shut that diesel down at every delivery all day long seems it would cause more problems. Very different from gas engines.
A swather is a 14 ft wide (in my case) lawn mower that cuts hay and puts it in swaths on the field so it can dry.