Google Adwords announced the availability of a new ad rotation setting that will show advertisers' ads that are most likely to receive conversion.
Previously advertisers were able show ads that were expected to receive more click activity or select to show/rotate ads evenly. Rotating ads can certainly inform advertisers quickly about what results in the highest numbers of clicks, and selecting to optimize for clicks can certainly increase traffic (both of which are common goals of some advertisers). Neither option however guaranteed more conversions would result. That changes with this new Adwords feature.
The new "optimize for conversions" option shows ads that are more likely to receive conversions. The option is applied to ad groups so you may only want to use this feature if all ads in one ad group are connected to one conversion event (a specific type of sale, lead, etc.).
Advertisers need to have Conversion Tracking available in their account to use the new feature. Data from tool is used to determine which ad is most likely to receive conversions. Also keep in mind that once the "optimize for conversions" feature is enabled, it will apply to all ads appearing on Google's search and display partner sites.