This opens up all kinds of scenarios.
What if the employee uses company truck to commute for conducting personal business either during the day or on the way to work or on the way home. By doing so he may save time (time he could have spent working) by not having to drive back to shop, office or even home to get his personal vehicle to use for his personal business.
Personal business could be anything from a doctor appointment, to going to a childs school function, picking up dinner for the evening, stopping to use a restroom.
Someplace it has to be determined what is acceptable and what is not, as well as if it is acceptable at what point are you on company time and when are you on your own time even though you may be in a company vehicle.
Rules are much simpler when the workplace is a fixed location. When it varies all the time it gets complicated. One job may be closer to home than the shop, but the next one is not. Then there is traveling to a job where you will not be coming home and have to spend the night, somehow it must be determined when you are on the job and when you are on personal time, yet you are essentially representing your company the entire time you are there.