The modern fleet car or van is infinitely more complex and powerful than those of a few years ago. Mechanical reliability has increased substantially, despite the servicing schedules tending to reduce due to better design, build quality and more advanced lubricants. In some cases there can be an issue about getting everyone involved to remember that car or van is a potentially-lethal weapon, and must be kept in good order. There are very important safety issues, as well as cost and commercial issues at stake.
So what is "fleet maintenance"? Large fleets frequently break this down into different types of maintenance, but many smaller fleets would find this unnecessary. It is good practice to try to balance between recording as much detail as possible, and finding the resource to do it. But keeping an eye on the detail can occasionally pay handsome dividends.