Well, look at my signature block please. I just purchased my 2014 Silverado 3500 dully. A couple days ago I just needed to move the trailer from one side of my drive way to the other to make room for a 20 foot dumpster (we're getting ready to remodel more of our house).
I thought I'd "fudge" since I was only moving the trailer a 50 feet and then back again to the other side of the drive way. So I did not use my weight distribution bars. (This was actually a good test). I went ahead and hitched up, and to my surprise, my rear bumper came down 2 inches! I was shocked.
I went ahead and moved the camper. I then put the weight distribution bars back on and the truck as I was going to move the camper again after the dumpster arrived. When I did this, the bumper raised about 1 and 1/2 inches. So from the original starting position, the rear bumper dropped only 1/2 inch with the bars on.
Lesson learned, I need the weight distribution bars when towing on the road! I'm glad I've got them... And yes, I have a brand new 1 ton dully (Chevy) 3500!
Word of advise: Don't leave home without them.