Anyone who uses a vehicle for more than just basic transportation. For example:
Trailer owners
To support weight and stabilize suspension.
Salesmen
To support weight of samples, catalogues etc.
Holiday makers
To support weight of passengers and equipment.
High performance enthusiast
Suspension stability and chassis tuning.
Maintenance fleets
To support load of tools and repair parts.
Military vehicles
To improve steering, handling and stability to the extent that the vehicle is safer.
Recreational vehicles
To support load of permanently mounted equipment and accessories.
Four wheel drive
To prevent suspension damage.
Front mounted equipment vehicles
To support load.
Ambulance fleet
To maintain stability and comfort for patients and staff.