Disables "fast boot". Useful if you are pushing group policy objects that are supposed to run on system startup as the system startup gets skipped with fastboot enabled.
Fastboot should be enabled on your computer by default. Allows the machine to perform a hibernation of the Windows base components upon shutdown instead of performing a full shutdown each time. This lets the machine resume the state next boot and start quicker rather than having to fully initalise everything each boot.