While we create a modern site we get the below two option to choose the group type :
- Private Office 365 Group
- Public Office 365 Group
Default selection is Private Office 365 Group meaning no one can join to the office 365 group until group owner(site owner) ** allow them to in, on the other hand in **public group anyone can join to the group without group owner approval - meaning,
any member can join and have Add/Edit/Delete access to all the assets of an Office 365 Group (SharePoint Site, Planner, Calendar, Teams) but these access cannot be granted to anyone without group owner approval in case private group.
Details description about the public and private group
Public Office 365 Group
Public Group means everyone can join it freely without obtaining permissions from the Group Owner. In other words – free lunch for all. Any member can join and have Add/Edit/Delete access to all the assets of an Office 365 Group (SharePoint Site, Planner, Calendar, Teams). I honestly do not see many uses cases for such groups. Might work for an all-company site/calendar if it is a small business, but with larger companies might lead to Wild West.
Private Office 365 Group
This is the default privacy setting when you create an Office 365 Group. Essentially what that means is that Group Owners control access to an Office 365 Group. You won’t be able to join one unless Site Owners let you in (add you to the group membership). The majority, if not all Office 365 Groups in your organization, will be Private.
For details understanding the private and public group, you may refer the below article :
Public vs. Private Office 365 Groups