Generally there should be some relationship between actual activity (based on actual kilometres or engine hours) of a vehicle and the way fleet operators obtain their plant/fleet income, which is often based on labour hours (income units) associated with the plant. Often however, fleet managers look only at income units to see if they have sufficient, whereas it is often the case that there are in fact a substantial number of income units attributed to a plant or fleet item but little actual use of the item.

A typical case is in the infrastructure construction industry. Construction supervisors are often up against tight deadlines to deliver projects, so they will take equipment to site and charge it to the job 'just in case' it is needed ahead of time. However the job may not actually require the equipment until well into the timeline and so the item sits unused for most of the time.

In this case, income units will be high but the actual use of the unit will be low - giving a false picture and leading to unnecessary costs.