MyBook Studio II -- Would the LED turn off when computer power off?

I turn off my Mac and the LED on Studio II become blinking (every 4 sec).  According to user manual, it goes to sleep mode.  Can it be completely turned off (with the LED off) without unplugging from power socket?  Or is it necessary to turn it off rather than let it in sleep mode? 

It means that the drive is in stand-by, it is not mandatory to turn it off.

Thanks Vadir.  But seems a bit not comfortable that the hard disk is not completely 'turn off ’ though I know it stops running when in standby mode.  BTW, what is the purpose of power button at the back?