At the end of March 2018, Google will be making a couple of changes to the way ad rotation works, and we've updated the Marin platform to support these changes.
First, we've tweaked our Ad Serving (Ad Rotation) options in the platform to streamline the choices to just two: Optimize or Do Not Optimize. The former of these will use machine learning to identify the top-performers in your ad groups and serve them more frequently, while the latter will simply rotate your ads indefinitely.
The next change we've made to the Google Ad Rotation options is the move from campaign-level management to group-level management. At the end of March 2018, all of your ad rotation settings will need to be configured from the group level, so the Use campaign level setting you see above will no longer be available.
For more information about Google Ad Rotation in the Marin platform, including how to make changes in both single-edit and multi-edit mode, please read our dedicated Support Center article.