1990 allegro motorhome what is the purpose of the air bag shocks?

To give extra support when carrying loads over the rated payload of the normal suspension (eg. leaf and/or coiled springs). The air bags can be inflated to various pressures lifting the chassis higher, to avoid bottotming out the suspension. Some of the Allegros came standard with them, but can be added via aftermarket products. Great addition to any vehicle carrying loads.