What follows is the description of all the server roles that might be installed during the ConfigMgr server deployment.
The site server role is always installed during ConfigMgr deployment. It is not possible to change preferences of this role or remove it.
The site system role is always installed on a computer that provides specific functions for the ConfigMgr environment. It is installed by the ConfigMgr server installer and if any ConfigMgr server role is going to be installed on an operating system.
It happens, for instance, when the administrator installs a Reporting Service point. During role installation, the installer configures the site system role as well as the Reporting Service point role:
Site system role configuration
The role might be installed on more than one operating system. It is most common in larger environments where each server role is on a separate operating system. In certain circumstances, we might change...