Calendar Teams are designed to allow groups of employees to be created to simplify viewing of status in the main calendar.
As an example, a group of key staff could be created to enable them to view each others leave status even though they are not subordinates of each other or part of the same sub team
Note that a calendar team can be created with different access permissions so that a member of a group may not necessarily see the other members. This capability is controlled by the section "Who can access" and group members which are included will be able to see the Calendar Team when selecting employees under the Calendar menu.
Also note that access to a calendar team does not provide further visibility of leave or employee details, that access is dependent upon the employee's manager/subordinate status.