Having full root-level access signifies that you'll be able to access and modify any kind of file on a selected server, which includes all the system files, and to change system settings or set up server-side software which may be required by specific scripts and even offline applications to work appropriately. A server is accessed at the root level with a root user, who has full privileges to do any of the abovementioned things. Your root user may also create other users. For safety reasons, you're advised to have one more account for day-to-day tasks and to use the root account only if you actually need to do a specific task on the website hosting server. The root-level access function will give you full control of your server from any existing location, as long as you have the user credentials.