If you have air BAGS then you adjust those to level the coach left-to-right and for ride comfort (to dampen bumps to some extent).
I have a new 2017 31 foot Forest River Sunseeker with rear RideRite air bags. The unit has 4 slides (1 right, 2 left and 1 back/rear), so the left side is a little heavier. I have the right side at about 40psi, and the left side at about 75psi, which puts the coach perfectly level left/right and about 1/2-inch higher than if at 10psi (the minimum you'd want in the bags). If I set them both to 50psi (or whatever) the left left side is lower.
We recently got back from a 9 day trip from Dallas to Yellowstone and I played with pressures along the way, and found the ride is a bit better with more air in the bags (although below you will see that other suspension upgrades made more of a difference than the air bags). It also sways a bit less with more pressure (I noticed this a lot before I did other upgrades). I also like the rear a bit higher to keep the naughty bits a bit further away from the road (like the leveling jacks, etc.).
This all of course only applies if your air bags are not tied together (only one valve, so one unified pressure in both bags). If they are tied then it's pretty much for ride comfort and *some* weight control (air bags do *not* increase the carry capacity of the chassis, but they *can* put less weight on the suspension adding life to springs, etc.).
To use air bags to level, measure at the center of the rear wheel from the ground to the top of the wheel well (in a vertical line from the ground across the center of the wheel to the bottom outside of the well) on one side and then the other. Then adjust the air pressure on each side so that the distance is the same. If you have (rear) factory sway bars (which are weak) then another benefit of higher pressure could be less sway. Do not exceed the max pressure of the bags...for me that is 100psi.
Note that I ditched both of the wimpy factory front and rear sway bars, and installed heavy duty Hellwig sway bars which made a HUGE difference in sway (turns like an SUV), and upgraded the shocks to Koni FSDs which made a similarly large difference in overall ride over bumps on crappy roads (almost like an SUV). So now air bag pressure is just to level the coach left/right and raise the butt a bit.
2017 Forest River Sunseeker 2800QSF
2013 Ford C-MAX SEL towed