Technically, it will only be applied to those users that are licensed for it:
Required licenses and permissions
You must have Office 365 ATP to get Explorer or real-time detections.
Explorer is included in Office 365 ATP Plan 2.
The real-time detections report is included in Office 365 ATP Plan 1.
Plan to assign licenses for all users who should be protected by Office 365 ATP. (Explorer or real-time detections shows detection data for licensed users.)