Can you describe what the purpose of those third axles is?
Probably a tri-axle dump, they need that axle down to meet weight restrictions on so many pounds per axle. But you need to lift it to make sharp turns, otherwise you scrub that axle sideways (it’s usually the first of three rears) as the truck fights to go straight. Sometimes driver forgets to put it back down after turn (has to be back down in specified distance from turn).
Increased weight capacity and evens out the stress on the axles and frame.