It's just cool, I guess.
I can see it being interesting in terms of, for example, a work of conceptual art that focused brilliant moonlight on a point. I might go to see something like that around here, in the same way as I'd go see a Calder mobile or a fascinating sculpture (Stanford has a great Rodin collection).
I wonder how big a mirror you'd need to actually heat something. How much IR gets bounced off the Moon, if any?
If somebody starts asking for major cash to cure cancer with it, or otherwise take advantage of the Chronic Gullible, that would be another story.