Hibernation is a way to freeze current working conditions of your Windows machine for a long time. Unlike the sleep mode which uses minimal power to hold the corresponding data in RAM, the hibernation saves the working state to the hard disk and then completely turns off the computer. For example, this can be very useful if you are running some important processes, but there's a need to leave your computer for a while. This mode draws no power and therefore is ideal for laptops which have a limited power source and can't go into the sleep mode for long.
However, if you don’t use the hibernation, it just takes up a lot of space on your computer for no reason. In this case, you may want to use the Hibernation module of CleanMyPC to remove the hibernation file and reveal around 1 GB of disk space or even more. Don't worry, if later you decide that you need the hibernation, simply go to the same CleanMyPC module and enable the feature with a single click.