i think they may be referring to leveling the suspension for driving to compensate for the different weight after building it out. not so much putting rocks under the tires when parked
I am a firm believer in fixing a problem, not putting a band-aid on it. Are you overweight or are the springs weak?
Murphy is not kind and he bites at the most inopportune times.
you can still be in spec and ride low in the back. the suspension is built to work over a range of weights. if you are usually pushing towards the limit. then leveling it out can be beneficial