The Pros and Cons of Windows 10’s "Fast Startup" Mode

Why You Might Want to Disable Fast Startup

[...] Fast Startup also has its problems, so you should take the following caveats into consideration before enabling it:

• When Fast Startup is enabled, your computer doesn’t perform a regular shut down. Since applying new system updates often requires a shutdown, you may not be able to apply updates and turn your computer off. Restart is unaffected, though, so it still performs a full cold shutdown and restart of your system. If a shutdown doesn’t apply your updates, a restart still will.
  
• Fast Startup can interfere slightly with encrypted disk images. Users of encryption programs like TrueCrypt have reported that encrypted drives they had mounted before shutting down their system were automatically remounted when starting back up. The solution for this is just to manually dismount your encrypted drives before shutting down, but it is something to be aware of. (This doesn’t affect the full disk encryption feature of TrueCrypt, just disk images. And BitLocker users shouldn’t be affected.)
  
• Systems that don’t support hibernation won’t support Fast Startup either. Some devices just don’t play well with hibernation. You’ll have to experiment with it to see whether your devices respond well or not.
  When you shut down a computer with Fast Startup enabled, Windows locks down the Windows hard disk. You won’t be able to access it from other operating systems if you have your computer configured to dual-boot. Even worse, if you boot into another OS and then access or change anything on the hard disk (or partition) that the hibernating Windows installation uses, it can cause corruption. If you’re dual booting, it’s best not to use Fast Startup or Hibernation at all.
  
• Depending on your system, you may not be able to access BIOS/UEFI settings when you shut down a computer with Fast Startup enabled. When a computer hibernates, it does not enter a fully powered down mode. Some versions of BIOS/UEFI work with a system in hibernation and some do not. If yours doesn’t, you can always restart the computer to access BIOS, since the restart cycle will still perform a full shutdown.
  

https://www.howtogeek.com/243901/the-pros-and-cons-of-windows-10s-fast-startup-mode/