As part of the connection to an Office 365 Group the site's permissions will also be connected to the Office 365 group's permissions. This process will not take away any granted permission on the SharePoint site, but will allow the Office 365 group owners and members to have access to the connected SharePoint site.
- The Office 365 Group Owners get connected to both the site collection administrators as the site owners group: everyone who’s Office 365 group owner also has site collection admin permissions on the SharePoint site.
- The Office 365 Group members get connected to the site members group. Everyone who’s Office 365 group member is has the permissions which are granted to the SharePoint site’s Members group.
- Any other permissions granted on the SharePoint site stay as is (so for example viewers will still have view access, broken permission inheritance stays working as is,…).
- Permissions "flow" from the Office 365 group to SharePoint. Adding a person to the Office 365 Owners group will also make that person an Owner (even Administrator) of the SharePoint site.
- There a no permissions "flowing back" to the Office 365 Group. If you add a person to the SharePoint Owners group then that person is not an Owner of the group.