I have no experience with that thing, so let me admit that firstly.

However, I'd think:

1) Elevated from ground... think of bugs, insects, reptiles, etc. Mosquitoes driving you nuts in the tent? Go sleep in the cab of the truck, it's right there.

2) Possible use of vehicle climate controls through the rear-window of the truck.

3) Drier. Less moisture from dew, less damage to ground. Compare tent on ground to tent in truck bed if it rains. Or if it storms, you could just sit in the cab and listen to the radio. Maybe mobile charging of cell phones with car-charger or converters to power other devices from the truck, right there.

4) And yes, it is mobile. You could move it in the shade of trees as the sun moves to keep things cooler or warmer depending on what you want.

5) Can pack it up and leave it in the truck-bed when done, without having to drag a trailer around. Far cheaper than a "trailer."

6) Doesn't damage ground you are on as much, since it's low-footprint and you can shift your spot around as needed, especially say rather than smothering grass with a tent ontop of it that can't get light or water properly.

7) You can use both the cab of the truck and the tent for various purposes, and they are attached.

8) If you had an emergency and needed to leave, it looks like you could easily and safely drive the truck slowly somewhere with no issues, taking everything at a moment's notice.

9) The feeling of added security by being up in the truck bed rather than on the ground.

10) If you have a truck and that attachment, there's no reason you would put your tent on the ground unless you weren't allowed to drive there. Imagine you're caught in a storm, the wind whipping at tents, pounding on the textile surfaces; yet, you could just go get in the cab of a truck in like 15 seconds with power, mobility, radio, GPS, etc.