Occasionally, one usergroup isn't enough for a member. For example, you may have a group for moderators and a group for sponsors. What do you do when a moderator decides to sponsor, to ensure they can get access to special sponsor content while still being labeled as a moderator? Make sponsors be their secondary usergroup.

In order to do secondary usergroups, the secondary usergroups switch must be enabled at Admin Panel -> Settings -> Switches. Once the switch is on, the secondary usergroups selector will appear when you edit any member profile -- it'll be just below the primary usergroup selector. It's a mutli-select combobox so you can select any number of secondary groups with ctrl+click.

Secondary groups act as a bonus. If any of a member's secondary groups have permission to something which their primary group doesn't have permission for, they get that extra permission. If the secondary groups lack permissions that the primary (or other secondary) group does have, the member keeps the permission.