Hibernation mode needs a good amount of hard disk space as the size of the hiberfil.sys (file that stores the content of current memory) file could be in GBs. Your laptop or desktop needs more time to resume your session as your current session is stored on the hard disk (instead of memory). In case of power loss, the unsaved data is lost. Other than that, hibernation mode is a good option to use when you need to leave your system unattended for hours.