The idea isn’t simply to flirt with cataclysmic danger, but to bring a small object (they suggest a 10-meter object called 2008EA9 that will pass nearby in 2049) into a loop around the Earth so we can study it closely for a few years. If we can get the art of capturing asteroids orbitally down to a science, we could use it to temporarily make asteroids into Earth-bound satellites (orbiting at about twice the distance of the moon), mine them for minerals, and then send them on their ways.
