Well, what I meant was that if the tires' psi are at street level, then rubber/tire cannot absorb as much bumps/rocks as the aired down level?
I'm sure you've felt the difference between the tire's psi even on pavement. So, the impact from every rocks (large or small) that you go over has to be absorbed at somewhere. If the tires are aired down, then, wouldn't that softness transfer less impact to the steering system (I know that shocks are there for a reason, but I'm talking about the impacts that are more than shocks can handle)?