Office 365 for Large Enterprise Automatically creating groups

“Beginning in March 2017, managers who have 2-20 direct reports, do not already have a direct reports group, and have permissions to create groups in Outlook, will automatically have a private group created for them with their direct reports. The manager will be added as an owner, and the direct reports of the manager will be added as members by default. The group will be named "<Manager's Name>'s direct reports", but that can be edited.”

“To help managers collaborate more effectively with their employees, we will automatically create Office 365 Groups containing the manager's direct reports. Managers can easily update, delete, or modify the group at any time.”

https://support.office.com/en-gb/article/Manage-automatic-creation-of-direct-reports-group-Admin-help-8387f129-19cc-4426-9911-e36fa0a01043?ui=en-US&rs=en-GB&ad=GB

How to Opt out:

https://support.office.com/en-gb/article/Manage-automatic-creation-of-direct-reports-group-Admin-help-8387f129-19cc-4426-9911-e36fa0a01043?ui=en-US&rs=en-GB&ad=GB