In principle, users may belong to none, one, or many groups (although in practice some systems place limits on this).
The primary purpose of user groups is to simplify access control to computer systems.
In practice, that would be very impractical – every time a student or staff member arrived, administrators would have to allocate permissions on every directory.
Joinable groups are not intended to be used for access control, but rather for such purposes as electronic mailing lists.
All users which match the search criteria will be considered a member of this dynamic group.