Why you need them – Without these, there is a potential of experiencing failure in your Windows 7 OS Deployment process \ seeing devices in Device Manager that you know have drivers available to them but aren't properly installed.
This happened previously with Windows Vista and is now being seen on some Windows 7 systems that do not have the 1.11 version of KMDF and the 1.11 version of UMDF This is great for the IT Professional until a driver is written to a specific version of the KMDF\UMDF which your system may not currently support.
KMDF\UMDF is provided by Microsoft to allow component drivers to leverage the framework to minimize what is needed to be included with the driver. WDF defines a single driver model that is supported by two frameworks: Kernel-Mode Driver Kernel Mode Driver Framework (KMDF) and User-Mode Driver Framework (UMDF). The Windows Driver Frameworks (WDF) is a set of libraries that you can use to write device drivers that run on the Windows operating system.