Power Supply Switch



How do i correctly turn off my pc before clean dust of my pc case ? Shoult after shutting down my pc push psu power switch and then unplug power cord or only unplug power cord? OR only shut down my pc?
I ask because there is a warning written in my psu's manual: "Please do not plug out the AC power line when the Power Supply is in use, even in a flash quick manner will cause damage to the components"(i use chieftec CFT-650-14CS on a high-end pc).
When i shut down a pc, the light of my mouse is blinking . it means pc is using a little power. Any professional advices ?
That means please don't unplug the power cord before turning off the power supply because unplugging the power cord before turning off the power supply "might" result in damage. I've seen similar warnings before but have never actually read about someone having that problem.

I usually shut down the pc the regular way. Then I turn off the power supply. Finally I remove the power cord. It's not just a safety issue. I have to remove the power cord and all the cables because I move the pc away from my desk in order to clean the interior. Take it outside if using a can of compressed air to clean the interior.