SPX STONE 2P4W WITH DPO CHECKS

Load drift is the short answer. When the valve shifts to neutral or center position, the dual pilot-operated checks lock the cylinder ports so the load just sits there and holds position. Without something like that built in, hydraulic cylinders can creep under load, especially if there's any internal leakage elsewhere in the circuit. Having those checks integrated into the valve assembly also means you don't have to plumb in separate load-holding valves on the outside, which keeps the circuit cleaner and cuts down on potential leak points.