Helium-3 is a substance that is very useful for nuclear fusion, which can generate a lot of power. Unfortunately we don't have a lot of it on Earth, but on the Moon it can be processed from basic moon rocks. Say that we figured out a way how to mine large amounts of the stuff in relative safety, but we still need to process the rock into Helium-3 Where would be the best place to do that, on the Moon itself or on Earth? The ratio of moon rocks to Helium-3 is not that spectacular (according to Popular Mechanics a patch of three quarters of a square mile to a depth of about 9 feet nets about 220 pounds of Helium-3), and moving enough moon rocks to Earth for processing is rather costly. Moving the processed Helium-3 back to Earth would require a lot less moving things around in space ships. However, it would require the facilities and knowledge to process this to be present on the Moon.
So which is the more viable option, to move all the moon rocks back to Earth and process them here, or have the processing done on the Moon and move the Helium-3 back here?