I guess its to make your litter boxes more pretty and less like a litter box. Until someone walks over to look at your indoor 'garden' and they're like "what are these little brown balls? Is that...bunny poop?" Then they realize its a litter box.
I mean, no one wants to see a litter box, whether it be for rabbits or cats. We all have litter boxes, so its not like WE care, but maybe people who don't have animals?
I'm sure you would have to change the box as often as a regular one, and probably replace the plants often because they would get nibbled to nothing.
It would look nice in a sunroom or something, but it seems like a strange thing to me. And if you have to go out and buy all the things for that, then maybe a waste of money. If you had all the materials to make it and you didn't have to pay for it, sure.