Having root-level access to your server means that you'll be able to view and change any file on it, which includes essential system files. You can also set up software that can update certain settings on your server throughout the, so that the installation is possible only if you are logged in as the root user. The aforementioned has full privileges, i.e. you will have full control over the machine at any time and you will be able to do anything you would like. You can also create various other users either with the same rights or with fewer rights, according to what you want them for - daily tasks, other server admins, etcetera. To be on the safe side, it is generally recommended to employ the root account only when you really need it and not for tasks which can be done through 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 control it at the root level.