Groups are a great feature but you may not be ready for them, want to create training material before giving them to user or only allow certain users to create them.
The PowerShell script to do this is based on the Outlook Web Access policy for your organisation but you can also create other and assign them to users if you want.
set-OwaMailboxPolicy -GroupCreationEnabled $false -Identity OwaMailboxPolicy-Default
What is important here is that it does not remove Groups, it only prevent users from creating them. Here are some screenshot of the experience to the user