A fleet vehicle is useful when it can complete its assigned work and be ready for what follows. Operating function covers that whole cycle: preparing the vehicle, reaching the job, carrying the right people or equipment, returning, and handing it over. A vehicle can run perfectly yet fail the assignment because it arrives without the required tools or cannot enter the delivery site.
The practical test is a representative working day. Follow the vehicle through the stops, waiting periods, loading tasks, and changeovers it will actually face. That reveals gaps which a specification sheet or a count of vehicles in the yard can miss.