After spending only ten minutes on the phone with the guys over at Slam Specialties it was obvious that they agreed wholeheartedly about this. Here's what they had to say:
Shock absorbers are an integral part of any suspension system. No matter what type of system you have, when you break down your suspension into its various parts it's easy to see the direct function of each component.
Springs: Whether leaf, coil, torsion bar, or air spring, their sole function is to lift or support the weight of the vehicle. Spring rates come into play in various guises but, ultimately and in its simplest form, the spring pushes the vehicle up to the desired height. Springs are not designed to absorb shock or provide damping in any way; which is why you'll see older vehicles, even with steel springs, "float" down the road.
Shocks: Shock absorbers are what actually control the movement of the vehicle's suspension under driving conditions. Properly set-up shocks allow for precise and predictable control over your vehicle; whether cruising, accelerating, braking, or cornering. In air suspension systems, shocks are also important for other reasons. Because air is compressible, and airsprings are essentially flexible pressure vessels, the spring rates vary. This variance is dependent on the height of the spring and the pressure inside. In most cases, this variability, along with the inability of the airspring to damp shock, causes the vehicle to bounce continuously after hitting an irregularity in the road. Bouncing can unload the tires and make handling difficult, if not dangerous. Shocks damp potential bouncing and allow the suspension to normalize very quickly keeping the contact patch of the tire pressed firmly against the road. This, in and of itself, allows the driver to remain in control.
Now, I know what you might be thinking-"I run stiffer 'bags and don't need shocks." While a 'bag with a stiffer spring rate inherently helps to damp shock to the suspension and reduces that bounce effect, they are no replacement for a good set of shock absorbers. Utilizing a properly set-up airspring and shock combination not only will give the safest ride but, in most cases, will also give the most comfortable and longest lasting. In any case, when setting up your suspension, always remember to work within the parameters of the components that you are using. Airsprings and shocks have the ability to work in a variety of situations. The keys to success when working with them are simple. Select the size and capacity of the components to fit the vehicle, make sure the angular travel of the airsprings are within manufacturer limitations, ensure that the air springs and shocks have adequate clearance throughout their range of movement and don't over-extend or bottom out either the 'bag or the shock.
Bottom Line: Shocks and air springs should ALWAYS be used together.