Google's advertising requirements can be summed up by Google's Advertising Principles. They are put in place to provide a positive experience for users.
https://support.google.com/adwordspolicy/answer/1316548?hl=en
Google, as a third party vendor uses cookies to serve ads on our site. Google's use of the DART cookie enables it to serve ads to our users based on their visit to our site and other sites on the Internet. Users may opt out of the use of the DART cookie by visiting the Google ad and content network privacy policy.
We along with third-party vendors, such as Google use first-party cookies (such as the Google Analytics cookies) and third-party cookies (such as the DoubleClick cookie) or other third-party identifiers together to compile data regarding user interactions with ad impressions, and other ad service functions as they relate to our website.