Actually it depends upon the quality of the service of the providers, though an un-managed server, you only get OS reinstall support from the hosting, and network and hardware support, with fully managed server and hosting, you can also ask your hosting company or server management company to do tasks on your control panel, OS, like PHP version upgrades, installing any modules etc, so if you are not much familiar with the OS, then its always recommended to get a fully managed server or hosting.