You need a server administrator to:

• Setup and fine tune your server for particular tasks. You can chose among lots of operating systems (Windows, Linux, BSD, etc.) and software packages.
• Keep your server software up-to-date and consistent.
• Fix and prevent problems that might occur due to software or hardware failures.
• Manage services, user accounts and all sort of configuration.
• Backup critical data constantly.
• Save money that you spend on a staff administrator salary.