To turn off your computer there are mainly 3 options on a Windows system – shut down, sleep and hibernate.
Shut Down completely stops all currently running programs and turns off the computer. On next boot, you will manually open any documents or programs you were using before the shut down. Shut down is preferred when you are done with your work and can let the computer sleep peacefully! You do not want the computer to remember what you were doing earlier. When you start the computer next time, it is a fresh start.
Sleep (Standby) saves all open documents and programs. Sleep also allows for the computer to quickly resume full-power operation (faster). Sleep requires a small amount of power to maintain itself. Typically, this process occurs within several seconds. When put into sleep, the computer immediately stops what it is doing and is ready to start again when you want to resume working. Use sleep if you want to turn off your laptop for less than 1 hour or so, for example when going for lunch or a tea meeting.
Hibernation saves open documents and programs to the hard disk, and then turns off the computer. When you are ready to use the computer again, the computer comes out of hibernation in seconds (fast). Then, the computer restores all the open programs and documents that were saved. Hibernation does not require any power to save the state of the open documents and programs on a mobile computer. You should use hibernation on a mobile computer when you know that you will not use the mobile computer for some time or when you know that you will be unable to charge the battery during that time.
The computer stores a copy of the system memory on the hard disk when the system hibernates. The file, Hiberfil.sys, is a hidden system file located in the root folder of the drive where the operating system is installed, In most cases it is C:\hiberfil.sys. The size of this file is approximately equal to the amount of random access memory (RAM) that is installed on the computer.
If you do not use the hibernation power setting, you can remove this file to free up disk space. Removing this file will disable hibernation. So, if you use hibernation on your computer, do not remove this file.
Sometimes, when using the Disk Cleanup program to free up some RAM, the hibernation file also gets deleted. To re-enable hibernation, type powercfg.exe /hibernate on at the command prompt or in the run window and then press enter. You need to have administrative privileges. Please refer to the MS KB article for more information.