I was looking at my Google Analytics stats, and I just though of another benefit for Google to do this. Since Google Analytics will get information about referrer for any site that has the Analytics script embedded in the pages, Google could increase the number of sites that get crawled.
For example, site X is not being crawled by Google, because it has not been submitted to Google, or it there are no links (that Google crawls) to it. Site X links to site Y, which has the Google Analytics script embedded. When a user clicks on the link from site X to Site Y, now Google will know to crawl site X.
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