The Robo-bee achieves such capability thanks to the phenomenon known as electrostatic adhesion, which is a similar process that allows statically-charged balloons to stick to walls. As for the Robo-bee itself, it is a programmed drone, and will measure no larger than the size of a 10 pence coin.
Dr Mirko Kovac, director of the Aerial Robotics Laboratory of Imperial College, London, claims that similar robots are currently undergoing trials in environmental monitoring and disaster-relief efforts. With such small robots flying around, you know that they do not have all that much electricity to work with in the first place, so hovering around is not going to be too efficient in the long run. Hence, the very idea of perching is appealing, as it provides an energy saving solution to the challenge.