Having root-level access to a server means that you'll be able to view and change any file on it, which includes essential system files. You may also set up software that can update particular settings on the server throughout the, so the installation can be done only if you're logged in as the root user. The latter has full privileges, i.e. you will have full control over the machine at any time and you will be able to perform anything you need. You can also generate various other users either with identical rights or with fewer rights, depending on what you need them for - daily tasks, other server admins, etcetera. To be on the safe side, it's generally recommended to employ the root account only when you actually need it and not for tasks you can do using other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect with the server and to manage it at the root level.