Should I turn on fast startup Windows 10?

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.

What does fast startup do in Windows 10?

The Fast Startup feature in Windows 10 is enabled by default if applicable. Fast Startup is designed to help your computer start up faster after you shut down your computer. When you shut down your computer, your computer actually enters a hibernation state instead of a full shutdown.