Unlike Fast Startup in Windows, the Fast Boot setting bypasses some of the initial tests your computer runs when it first starts up. Anyone who needs regular access to the BIOS—like overclockers—might ...
Fast Startup on Windows is meant to speed up the boot time. By putting the computer into a hibernation-like state by saving the system state to the disk, the next startup is faster than a cold boot.
Saving 5 seconds isn't worth the potential problems.