Because it’s so easy for users to create Office 365 Groups, you aren’t inundated with requests to create them on behalf of other people. Depending on your business, however, you might want to control who has the ability to create groups. Why do this?
This article gives you the steps to turn off the ability to create groups in all Office 365 services that use groups: Outlook, Planner, SharePoint, Yammer, and Microsoft Teams. Only the people who are in a security group that you create will be able to create Office 365 Groups in these apps.
To control who creates Office 365 Groups, you use Windows PowerShell, which is a lot like typing commands at the C:\ prompt in the old DOS environment. If you’ve never used PowerShell, this task is a great introduction to using it. We walk you through what you need to do, step-by-step.
http://www.cloudguy.pro/restrict-office-365-group-creation-the-hidden-feature/