Another use case is invasive species control in parks and large public lands. As an example, Portland has a large park that stretches along a ridge-line for about ten miles, and it's getting overgrown by English ivy, which kills the trees. It's a big enough area that pulling it all by hand would be very expensive. Ivy-pulling robots would be pretty awesome, but it's a hard problem. Vegetation is thick and the terrain is everything but flat. You'd probably need some giant hexapods or something just to move around, and maybe some kind of Ivy-grabbing appendage.

Just mapping out the ivy infestation with drones and image recognition software would be impressive. There's enough room for a quad-rotor to move around in theory, but it would have to have some pretty sophisticated obstacle avoidance algorithms.