Why is it necessary to unplug peripherals while cleaning PC

_Jurt_

Honorable
May 16, 2017
15
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10,510
Hello everyone,
I know my questions may be a bit paranoid, but I'm really new to the whole desktop thing. Few months ago, i wanted to clean fingerprints left from assembly on my AIO pump head. I made a post where i asked about the procedure (here it is http://www.tomshardware.co.uk/answers/id-3652231/cleaning-aio-pump-head.html). In short i switched off the PSU, opened the case, grounded myself to the PC case and wiped the pump head with lint-free cloth (i have read that they are not likely to develop ESD + the pump head should not be ESD senzitive). It all went well and there aro no apparent problems with the PC afterwards.
This day though i decided to clean my PC of dust. I have read a lot of guides on it and most of them stated that you need to unplug all peripherals (monitor, keyboard...) before opening and cleaning the PC. This left me a bit scared because when i was cleaning the pump head, i didnt disconnect anything, thinking that it is not necessary when everything is off and there should be no power running (PSU was turned off).
My question is then-were my precautions enough and i am simply worrying too much when everything is fine, or is there any way i may have damaged my system by not disconecting the PC peripherals (even latent damage counts)?
Update: just updated my language in the post to make it less confusing.
 
Solution
Unplugging the power supply from the wall is all you have to do.
Unless you need to move it to clean it their no real reason to unplug everything.