To extract H-3. It can be used as a rocket fuel I believe. Harvesting it from there means that the amount of fuel needed to get to the moon (or any heavy lift effort) would be cut in about half. If you can make fuel in a low gravity environment, you do not need the fuel to go home when you leave. That means you can either take more stuff with you, or you can lift off with less fuel—it just makes the whole process more efficient.
Wiki
Commercial demand for tritium is 400 grams per year and the cost is approximately US $30,000 per gram.