I would say fuel economy, but since your half ton is a gasser and your one ton most probably a diesel, that wont fly...
Had a feeling that mileage would be brought up, and you're correct.
With the 3500's diesel it tends to average around 10 mpg, with a very rare occasional fill-up in the low 13s. That may sound dismal, but considering the terrain, that it's always pulling something, and the speeds, it's not all that bad.
Meanwhile, the 1500's best tank has been 14.75 mpg, and the lowest 12.89. But, except for the 20-mile drive pictured above, it hasn't been used for towing. Or carrying more than five bags of softener salt in the bed for that matter.
When towing that trailer with the '14 1500 the mileage dropped to about half of normal (into the low teens). Don't remember what the Lie-O-Meter claimed during the short drive with the '21, but it was likely heading for the low teens, too.
So in my case there's no reason to compromise safety (tiny brakes, no exhaust brake, etc.) to save on fuel. Besides, it wouldn't be all that easy to put a gooseneck hitch in the 1500.