To do a round-trip mission from Earth, it takes more energy to land on the Moon and return than it takes to go to a lower mass object like a half-kilometer diameter asteroid, grab a sample, and return. However, it takes longer to go the greater distances to the Earth's orbit Lagrange points.
Earth "trojan" asteroids have been looked for, and, so far, only 2 have been found. According to Wikipedia
https://en.wikipedia.org/wiki/Earth_trojan :
"An Earth-based search for L5 objects was conducted in 1994, covering 0.35 square degrees of sky, under poor observing conditions.[5] That search failed to detect any objects:
"The limiting sensitivity of this search was magnitude ~22.8, corresponding to C-type asteroids ~350 m in diameter, or S-type asteroids ~175 m in diameter."[5]
In February 2017, the OSIRIS-REx spacecraft performed a search from within the L4 region on its way to asteroid Bennu.[6] No additional Earth trojans were discovered.[7]
"In April 2017, the Hayabusa2 spacecraft searched the L5 region while proceeding to asteroid Ryugu,[8] but did not find any asteroids there.[9]"
Of the 2 discovered so far, one is estimated to be 150-to-500 meters in diameter and the other is estimated at 1100-to-1260 meters, both at L4.
While it is conceivable that asteroids of this size might be moved to Earth orbits if they turn out to be more firmly compacted than the asteroids we have been able to visit and sample or impact, so far, there would be some serious hazards associated with bringing a kilometer wide asteroid to low Earth orbit - some sort of guidance of thruster malfunction, such as we have seen in multiple recent launch and landing attempts, could put that asteroid on a collision course with Earth.
So I expect initial visits will be scientific missions with sample return, and any mining missions would probably be scaled-up "samples" using similar strategies.
Perhaps, some day, materials could be landed on the Moon for refining before descent to Earth's surface, or even refined in orbit around Earth or even out at L4 or L5. But, it is a tradeoff between getting the raw materials to Earth's surface vs getting refining and perhaps manufacturing infrastructure equipment out to where the raw materials currently reside so that only finished products need be descended to Earth's surface.