We had customers that we delivered to on a regular basis because we specialized in furniture.
A few drivers had dedicated routes to serve a certain group of customers. For instance there was a couple of drivers who only did Nebraska.
A few drivers only did Texas. Some only did Chicago and Wisconsin.
I served many customers more than once but I didn't do exclusive territories. I delivered loads to different places each trip out. We had multiple stops on most loads out. Because of this, it didn't take long to start visiting customers more than once even though I didn't have dedicated routes.
Many other trucking companies that haul regular freight are set up differently though. They go where ever the highest paying loads take them. Of course those same companies also have dedicated positions.