Howdy,
I suppose it has some to do with your tongue weight, 2500 or 3500 truck, and trailer GVWR. I towed a bumper pull with a 2500 that had a 1000 lb tongue weight with weight distribution for years then decided to haul a golf cart in the bed of the truck which did max out the truck. I added air bags & Hellwig stabilizer bars, hitched up as usual then added air to final level. Worked great for several years and many miles using both weight distribution and air bags.
There is an ultimate purpose for weight distribution in general though. I found this video a while back that's pretty good at demonstrating the different effects between air bags and weight distribution.