There are proposals and maybe serious plans to send astronauts to asteroids or Mars' moons, objects which are a few kilometers or just a few meters in diameter. I call them "milligravity" objects since their gravities are operationally relevant, but maybe medically equivalent to microgravity. Some of those objects should be loose rubble piles, never before encountered by humans.
Wouldn't it be a valuable preparation to launch 20 tons or so of such a rubble pile, a bunch of sand and rock loosely bound together, to (a short lived) low Earth orbit and have astronauts test out handling technologies and operations on it? The structure of the specimens would be completely controlled by design. It could have sensors planted inside of it. The operations could be performed in relative safety. No time consuming transport of some boulder on some NEA would be needed, as with the ARM mission. A boulder which could be picked up from a NEA won't be an exotic rubble pile anyway, I suppose it would be more like some meter sized meteorites found in museums on Earth's surface.