[ProCynic]

I think the idea is that you can use solar or nuclear to crack it into hydrogen and oxygen for use as rocket fuel. With rockets, fuel is both energy source and reaction mass, meaning that you throw it out the back end and can't recover it. You can also use the oxygen for breathable atmosphere. Every kilogram of useful mass you can find on the moon is one less kilo you have to haul from earth.

[rbanffy]

You can also use it as propellant for nuclear thermal rockets. You can't lift off from Earth on one, but the Moon is an easier problem.