I never even knew that there was such an AdSense feature that would allow you to precisely specify which sites could actually use your Adsense code.  And I never even thought of a reason why anyone would want to use my codes elsewhere.

In my AdSense: Sites Authorized to Show MY Ads, I take a brief overview on what this means, how it might impact us, and how to set up your authorized sites for AdSense, if you wanted to.