You need turn off power to all system devices is when you do the following:
Replace or add hardware
Move the system from one location to another
Prepare for an expected power outage or natural disaster like an approaching electrical storm
System devices to power down include the CPU, the monitor, and external devices such as disks, tapes, and printers.
Before you turn off power to all system devices, you should shutdown the system cleanly, as described in the preceding sections.
Select one of the following to shut down the system.
If shutting down a server, see How to Shut Down a Server.
If shutting down a standalone system, see How to Shut Down a Standalone System.
Turn off the power to all devices after the system is shutdown. If necessary, also unplug the power cables.
After power can be restored, use the following steps to turn on the system and devices.