A Microsoft 365 group is a membership service in the Active directory that allows you to connect multiple Microsoft 365 teamwork services.

Because the group provides access to other services like Teams and SharePoint, it is essential to know how it grants that access when you plan a migration or connect a SharePoint site to a Microsoft 365 Group.

To learn more about the interactions between a group and other services, see The relationship between Microsoft 365 Groups, Microsoft Teams, and other services.

In this example, we will look at a Microsoft 365 group with a connected team, planner plan, and SharePoint site.

Your owners and members are shared between the Microsoft 365 group, team, and plan. For example, if you add an owner to a planner plan, he will become an owner of the Microsoft 365 group, team, and any other plan associated with that group.

The associated SharePoint site uses the membership of your Microsoft 365 group. For example, if you add an owner to a group, plan, or team, that owner automatically becomes part of the associated SharePoint owners.

Additionally, these owners get site collection admin permissions.

Adding new users to these groups in your SharePoint site, however, does not add them to the Microsoft 365 group, team, or plans.

For more information, see the Microsoft article Site permissions after Microsoft 365 group connection.

When you migrate a site to a Microsoft 365 group-connected site, the user account you use for the migration, the owners, and the site collection admins of your source site are added to the owners of the destination group. The members of your SharePoint site are added to the members of your destination group.

For more information, see the Default behaviors section of Copy structure and content - Microsoft 365 Groups.