If the main power switch is turned off while the machine is accessing its HDD, damage can well occur on the HDD.
To avoid such damage, the machine is provided with a shut-down sequence.
MEMO:
When turning OFF the power of the host machine, be sure to press the power switch on the control panel for 3 sec or more, and then select "Execute" key on the
shutdown sequence screen. There is no need to turn OFF the main power switch.