Having full root-level access means that you can access and modify any kind of file on a particular server, including all system files, and to change system settings or install server-side software that may be required by certain scripts and even offline applications to work effectively. A server is accessed at the root level with a root user, which has full privileges to do all the abovementioned things. Your root user can also create other users. For safety reasons, you are advised to have a different account for day-to-day tasks and to use the root account only if you actually need to perform some task on your server. The root-level access feature gives you full control over your server from any location, given that you have the user credentials.
Full Root-level Access in VPS Servers
You're able to control your new VPS servers at the root level regardless of the package that you've picked, as long as the server is ordered with either the cPanel or the DirectAdmin web hosting Control Panel, or without Control Panel at all. In the first case, many system settings can be managed via an easy to navigate web-based interface, while in the second, you will need to make everything via a console, until you decide to set up a Control Panel yourself. In either case, you'll have full control over the VPS and any kind of system and custom content on it all the time, which makes this kind of hosting perfect for any application which you cannot run with a shared web hosting account because of the limited degree of access - frameworks, VoIP and audio/video streaming software, and many others. The last VPS Control Panel choice is Hepsia, however the root access to your server will be restricted.