Having full root-level access means that you can access and modify any kind of file on a selected server, including all system files, and to change system settings or set up server-side software which may be necessary for specific scripts and even offline apps in order to work appropriately. A server is accessed at the root level through a root user, who has full privileges to perform all of the abovementioned tasks. The root user may also make other users. For safety reasons, you're advised to have one more account for everyday tasks and to use the root account only if you actually need to do some task on your server. The root-level access attribute will provide you with full control of your server from almost any location, provided that you know the user credentials.
Full Root-level Access in VPS Servers
You'll be able to take care of your new VPS servers at the root level whatever the plan that you've picked, as long as the server is ordered with either the cPanel or the DirectAdmin website hosting Control Panel, or without any Control Panel at all. In the first case, many system settings can be controlled through an easy to use web-based interface, whereas in the second, you'll need to make everything via a console, unless you decide to install a Control Panel yourself. In either case, you'll have full control over the VPS and any system or custom content on it all the time, that makes this type of web hosting perfect for any app that you cannot run with a shared web hosting account because of the limited degree of access - frameworks, VoIP and audio/video streaming software, etc. The last VPS Control Panel option is Hepsia, but the root access to your server is limited.