What metrics estimate conversions that measure user behavior across devices and environments?
The correct answer is:
People own multiple devices that can access the Internet, and will often view your ads in one environment and then convert on another. Cross-environment conversion reporting shows the effectiveness of your advertising campaign across all environments (tablet, mobile, and desktop; app and web), regardless of the device or environment a user converts on.
Read more here: https://support.google.com/dcm/partner/answer/6163585