Having root-level access to a server means that you can view and modify any file on it, which includes crucial system files. You can also install software that can update specific settings on your server during the process, so the installation can be performed only if you are logged in as the root user. The latter has full privileges, which means that you'll have full control over your machine whenever you want and you will be able to perform anything you need. You can also create other users either with identical rights or with fewer rights, according to what you want them for - day-to-day tasks, other server admins, etc. To be on the safe side, it's usually recommended to employ the root account only when you really need it and not for tasks you can do via other accounts. You may 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.