A user group is intended to configure specific rules/restrictions for users or to assign certain desks/rooms to specific users. If you want to assign certain desks/rooms to specific users, it is also necessary to create an asset group in order to link the user group.
By default, all users in the system are in the group ‘Everyone’. If you want to set a rule that applies to all users, you can do this in this user group. If there are exceptions for a specific group of users or if you want to divide your users into departments, you always can add an extra user group.