Having root-level access to your server means that you can view and modify any file on it, which includes important system files. You may also install software that can change particular settings on your server throughout the, so that the installation can be performed only if you are logged in as the root user. The aforementioned has full privileges, i.e. you will have full control over your machine whenever you want and you'll be able to do anything you'd like. You may 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, etcetera. To be on the safe side, it is usually recommended to employ the root account only when you actually need it and not for tasks you can do 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.