Having root-level access to your server means that you'll be able to view and modify any file on it, including important system files. You may also install software that can change certain settings on your server during the process, so that the installation can be done only if you are logged in as the root user. The aforementioned has full privileges, which means that you'll have full control over the machine whenever you want and you can do anything you need. You can also create various other users either with identical rights or with fewer rights, based on what you need them for - day-to-day tasks, other server administrators, etc. To be on the safe side, it's generally recommended to employ the root account only when you really need it and not for tasks that you can do via 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 manage it at the root level.