I confess that I personally don't air down as far or as often with my XK as I did with my old LJ.

In the majority of Jeeping conditions the air-down advantage is predominantly about ride (like the above posters noted). My ride is already so much more cushy in the Commander that not airing down results in the same bouncing I got after lowering the LJ. So a lot of times I just don't bother, even though I carry a portable compressor in the rig for quick airing up.

On the other hand, there are Jeeping conditions that simply demand air-down. The clearance loss is minimal, and you get much better traction over rocks as the tire flattens out (and you lose the "bounce-off" and such, too). In those cases, I go down to 20 or so with my 285s. Nicely squishy with little chance of popping the rim.