A new ad rotation setting in AdWords lets you choose to show ads you expect to provide the highest conversion rate, rather than receive the highest click-through rate, Google announced via its Inside AdWords blog.
To use the new “optimize for conversions” setting, you must have Conversion Tracking in your account, because Google uses data from that tool “to determine which ad is the most likely to receive conversions.” If Google doesn’t have enough data to make a decision, AdWords will show an ad most likely to receive clicks.
After the “optimize for conversions” feature is enabled, it will apply to all ads appearing on Google’s search and display partner sites.