The requirement is that when someone is added to a specific group, then a notification will be sent to the Administrator of that group.

An administrator can be declared while creating the group. If the Admin field is left empty or if this notification option (that is described here) is disabled then no notification should be sent on the addition of user.

For the special 'confluence-administrator' group which has superpowers, the notifications can be sent to all the members of this group when a user is added to this group. From a security perspective, it is better this functionality should be enabled by default for this special group.

This functionality is useful especially the cases like the CVE-2023-22515 vulnerability caused.