My first encounter with looping came back in 1976. IE had the driver take the computer punch card and put it in the right order and break the blocks where it needed based on the driver's experience. Back then, it took 3-4 days (basically a week) each time a changes needed to take place!
As a preload and on-road supervisor I looped areas for my drivers based on their input and natural and area boundaries. The driver was also involved in setting up the car load diagram and the adjustments to and from.
I also was involved with the reloop of a new center that was moved to a different district and we had to loop areas to come from the opposite direction. This was going to be my center so I got the drivers involved with this project as well.