Having root-level access to a server means that you'll be able to view and update any file on it, which includes important system files. You can also set up software which can modify particular settings on the server during the process, so that the installation is possible only if you're signed in as the root user. The aforementioned has full privileges, i.e. you will have full control over your machine at any time and you will be able to do anything you would like. You may also make various other users either with the same rights or with fewer rights, according to what you want them for - everyday tasks, other server admins, etcetera. To be on the safe side, it's generally recommended to use the root account only when you actually need it and not for tasks that you can do through other accounts. You can use a web-based graphical interface or a Secure Shell console to be able to connect to the server and to control it at the root level.