[BinaryIdiot]

While I agree with you that wheels would be more efficient energy wise the problem there is obstacle avoidance (especially if it travels down a long path that is suddenly blocked and it has to return) (thus maybe it's not as energy efficient except for very direct and easy routes) and thievery. Flying solves both of those issues but is expensive energy wise.

I think we'll see this little by little in testing and, maybe in 5-10 years, one of this laboratory "break throughs" in batteries will materialize and drones will be able to fly very far away and this will become cost effective.