Fast startup was introduced in Windows 8 and uses session 0 hibernation to save the kernel state to disk. Reading the kernel state from disk is 30 to 70 percent faster than a full system initialization on most systems.
While fast startup should be beneficial in most cases, especially in combination with UEFI, it can also be problematic. For example, I’ve come across systems that refuse to connect to wireless networks without a cold boot, assumedly due to a problem with the reinitialized driver. But if an updated driver doesn’t solve the problem, you might want to disable fast startup.
Source : Petri