The System Administrator User Role has full hiring system access by default with all permissions turned "On." This User will therefore see all Locations, Position Templates, and Applicants whenever they login to the hiring system, as well as have the ability to make any necessary changes system-wide and at any time.
This User Role does NOT need Assignments. The only time System Administrators need set Assignments is if they wish to receive Notifications (which may be adjusted under their profile's Notifications tab).
The System Administrator User Role cannot be edited under Admin>User Roles, and is locked. This role is best reserved for members of an organization who need full access at all times, or are high-level decision makers for the rest of the team.