I use its functionality some times,to sit on and load stuff.
When I'm out off roading and we stop to eat, assuming I don't have tons of cargo back there, I'll slide it out and sit down and eat. Of course a chair works too, but I often forget to bring one.
I haven't had to carry too many heavy objects, but having it slide out, you don't have to strain your back leaning over to lift stuff in. You can probably just use the bumper like you mentioned to slide stuff in, but I would prefer not to scuff the bumper up. It's all personal preference.
Oh yeah, with the slide out tray and the rear seats folded down, you have a flat platform for carrying larger items.
It's very easy to remove, a couple members have done it, and Harper did a write up a while back.