Having root-level access to a server means that you will be able to view and change any file on it, which includes crucial system files. You can also set up software that can modify particular settings on the server during the process, so that the installation can be performed only if you are logged in as the root user. The latter has full privileges, i.e. you will have full control over the machine whenever you want and you can do anything you need. You may also make additional users either with the same rights or with fewer rights, based on what you want them for - everyday tasks, other server admins, etc. To be on the safe side, it is usually recommended to employ the root account only when you really need it and not for tasks that you can do using other accounts. You may use a web-based graphical interface or a Secure Shell console to connect with the server and to control it at the root level.