Airbag helper kids are useful to set suspension up where significantly varied loads are carried. In the case of leaf spring, vehicles particular care must be taken to ensure that they are used as a helper spring as opposed to something designed to carry a significant weight.
The reason for this is that the airbags cause a single point load on the chassis at a point that the vehicle manufacturer never intended for a load to be applied. In extreme situations, the Chassis can become bent or cracked because of incorrect application of this component. Despite this caution airbags can be useful particularly where they have an accessory kit added to them that allows them to be inflated remotely from within the cabin.
The caveats listed above are not as applicable for coil spring situations where an airbag is fitted within or inside the coil spring because In this type of suspension, single point loads are expected at that particular point.