Thank you for contacting Western Digital Customer Service and Support. My name is Bill.
I understand that you would like to know about the power button on your WD Elements Desktop device.
This power button was designed to be used exclusively in conjunction with WD Smartware Pro for Windows software.
This software however is End-of-life and no longer distributed or supported. You can turn the drive off by removing the power cable after safely ejecting the drive from your computer.