The house-sized sample would be dissected and provide valuable information for planetary defense strategies that may someday have to be used deflect a much larger NEO headed on a collision course with Earth. Capturing an asteroid would also mark mankind's first attempt at modifying the solar system to enable the permanent settlement of humans in space.
A long shopping list of space supplies could be extracted from a 20-foot asteroid: 200 tons of silicates, 100 tons of water, 100 tons of carbon compounds, 90 tons of metals: mostly iron, nickel and cobalt.
The material could ultimately be used to build, supply, and radiation-shield a manned outpost at the Earth-moon Langrage point 2, a sort of space "trucker's stop" on the way to the moon.
What's enabling about this approach is that the mission would make available 28 times as much mass for building space habitats as the mass required to launch the initial "space tug" for retrieving the asteroid.