Windows 8 Sleep Mode
Windows 8's Sleep saves your data to RAM and then switches to minimal power mode. There is a 4 second delay as Windows 8 switches back to normal power mode. In the event of a power failure you would lose any unsaved data which is stored in RAM (memory). At this point you will probably have to type in your password to resume after sleep; fortunately, 'Require a password on wakeup' is another configurable setting from the task list menu.
To be honest though, with Windows 8 starting up so fast, why not just switch it off?