When I had my Land Cruiser, I had all the leaf springs re-arched for higher body clearance. I had 36 " tires on it and I did a lot of serious four wheeling. The body lift kits people put on trucks are really only good for looks as they really aren't functional. There are proper ways to get good ground clearance.
Probably for better clearance when they are off-road.
Simply for the looks. It's cool. I am gonna do that to my first truck. Chevrolet too.