Air cushioning uses sealed air chambers or pods under your foot, similar to what you'd find in a high-end running shoe. The big advantage is excellent impact absorption with almost no added weight—air is lighter than foam or gel, so you get great dampening without making your setup feel sluggish.
The trade-off is that air cushioning can feel slightly "bouncy" compared to the more muted feel of foam. Some riders love the lively sensation, but if you prefer a deadened, planted feel underfoot, it might take some getting used to. It's also only found on select premium bindings, so expect a higher price point.
Air cushioning makes the most sense if you're riding lots of choppy terrain, taking big drops in the park, or dealing with foot fatigue on long days. For casual resort cruising, standard foam or multi-density cushioning will serve you just fine at a lower cost.