Auto-park is a safety feature that automatically returns the dock leveler to its stored position when a truck / trailer pulls away.
Why is this important? Hydraulic dock levelers are downward gravity biased. A hydraulic dock leveler moves up due to the energizing of the hydraulic system. When the system is powered off, the leveler's weight, combined with gravity, move it downward. A hydraulic dock leveler in its raised position will lower unless it is supported by hydraulic pressure, the truck bed or some other mechanical device (maintenance stand).
For a leveler without auto-park, when loading / unloading operations are complete and the truck / trailer pulls away, the deck and lip of a positioned leveler lower and come to rest on the leveler's bottom support stops. This creates a potentially dangerous recess in the dock floor. With auto-park, the leveler automatically returns to the "parked" position.