Type-1 hypervisors operate directly on physical hardware without any intervening operating system. Type-2 hypervisors run as an application installed on an existing operating system. Type-1 hypervisors perform much better than Type-2 hypervisors since there is no intervening layer to negotiate between themselves and the system hardware, nor do they need to contend for resources with another controlling layer of software. Why then are Type-2 hypervisors widely used? What are some of the use cases?