Over a year ago I put AdSense on a site that was getting limited traffic and only had a couple hundred indexed pages. Being this site was a directory, I should have had thousands of indexed pages. Anyway, I added the code into a global footer and forgot about it.

Then about a week later, when I was going over some SEO data I noticed my indexed pages had jumped to 25,000. All these new indexed pages had that global footer. Of course this led me to believe the AdSense ads had something to do with it. 

via Search Engine Journal