Hibernation saves the complete state of the PC and removes power.
The PC will appear to be totally off. This is the lowest power sleeping state available and is secure from power outages. When the end-user resumes from a hibernated sleep state, the BIOS will go through the normal POST and then read the hiberfile that was previously created to save the PC's state. The PC will then resume right to the very state it was in when the user previously entered hibernation. By using hibernate, the end-user will have a reduced startup time AND will not have to start applications, open files, or navigate to the pages they were editing or reading in files.