Yes, there is a legitmate reason why you would do this. It escapes me at the moment but... No, actually, I could see a reason. If your network connection was severed but you needed to back up the files on your Mac, this is a potential life saver. The idea is simple:
spoof simulate the .mac servers. Another use here would be setting up iPhoto's built-in web publishing tool (which would go to .mac) to publish to a local server, although there's a ton of work you'd have to do on the server end, in WebObjects, that would be no fun. Anyway, at the end of the day all this is would be a way to probably get in trouble. Don't do it. Neat to see though, isn't it? Nice work Otto.