One advantage for airbags is getting the rear back to unloaded height, which puts your headlights back into great alignment for nighttime driving.
Another advantage is that they give a better ride than leafs, in my opinion. Often, the rear springs ride pretty soft, especially in 1/2 tons. To me, the bags give a better ride than the leafs, with infinite adjustability to boot.
Keep in mind, if you raise the rear ride height, you will need to adjust your WDH to compensate.
It is nice to air them up for towing, then drop them down to 5psi and enjoy your stock ride while not towing.