Was talking to a Timpte Dealer today and he said if you are dumping at a high capicity facility where you can open both hoppers as fast as you can and them close them right away (where I haul grain you get out of truck and before you get the front hopper open one of the workers already has the back hopper open and then you can close them again most of the time it takes longer to get in and out of truck than it takes to dump both hoppers)it is probally a good idea if you are dumping slow or at an auger don't bother to dump the air.
I am a custom hauler in Canada,,,I run air ride tractor_trailer units,,,it is AlWAYS a good idea to dump the air when unloading at a high capacity elevator for all the time it takes, you save yourself money down the road.