• “Fast startup”, which is enabled by default on Windows 10 takes the state of the Windows kernel which is essentially the core elements of the operating system, and saves it to the disk. 
• However, this only happens after Windows logs you off so none of the data from programs or files you are working on gets saved. In this sense, it’s closed to a normal shutdown than hibernation but it doesn’t get 100% of the way there.
• The benefit of “Fast startup” is exactly what it sounds like. Your PC doesn’t have to spend tons of time reinitializing critical Windows components when you power the system back on allowing for shorter boot times. 
• However, there’s a downside that can cause really puzzling issues if you’re unaware that “Fast startup” even exists.
• Problems that are present within the kernel itself, such as a misbehaving device driver that would normally disappear with a full shutdown can recur when you start your computer back up if you have “Fast startup” enabled. 
• So, because Microsoft figures people are more likely to hit, “Restart” than “Shut down” if some bug necessitates the reboot, “Restart” actually cycles your PC through a full shutdown whereas “Shut down” counterintuitively does not.
• But there are ways around “Fast startup” if you want to ensure your computer is completely clearing out its current state every time your turn it off. You can do this by holding the Shift key when clicking “Shut down” from the Start menu.

There’s a chance you may not even miss the slightly faster startup if you’re running a modern system with a speedy SSD.

TL;DR Do “Restart” or Shift + “Shut down” once in a while for maintaining the optimal health of your Windows operating system.