Ah, it was the risk of lightning strike that I overlooked.
I guess if the plug is working properly then there would be no reason not leave the PC plugged in with the switch off at the wall. But then yoiu don’t know it’s not working properly until you get zapped so maybe it’s prudent to just unplug it.
It’s quite easy to detemine that the switch on the socket is working; if (like very many people) you have your monitor, PC, printer and scanner plugged into a four-way power strip (no doubt somebody will be along shortly to tell me how bad an idea this is), then the isolation of the live supply will be evidenced by lots of little lights going out, indeed many power strips have a neon indicator on them, which will also go out when the supply is turned off.
Leaving the computer plugged in with a switch on the wall to turn off the power is not as safe as unplugging the computer totally. It is very difficult to accidentally plug the computer back in. It is very easy to accidentally knock the switch back on. It is also easy to glance at a switch and think it is on instead of off. It is much harder to accidentally think the computer is unplugged.
Static electricity damages electronic parts because the person touching the electronic part is at a different potential than the electronic part. There is no reason to think that you as a person are at ground potential. If you have every be shocked walking after walking across carpet it is because you were at a different potential than the thing you touched. So leaving the computer plugged in to keep it grounded does not help reduce the possibility of damaging the computer with static electricity and it is potentially unsafe.
You and what your are touching have to be at the same potential. You and what you are touching do not have to have the same potential as ground. (In all probability, after you touch the case, you and the case are probably at ground potential.)
gazpacho makes some excellent points.
Things to remember:
In accidents there’s always a “chain of errors”. Somebody built something wrong, it didn’t get noticed in inspection, etc. and the next thing you have is a plane crashing in a corn field in Iowa. Assume that you are in the middle of a chain of such errors and that your one little mistake will complete it.
Computer PSs are made in east Asia by the Lowest Bidder Sweatshop Inc. The Lowest Bidder Sweatshop Inc. got the job over the Next Higher Bidder Down The Road Ltd. because they substituted a a resistor where a fuse really should have gone, saving .5 cents. The resistor they bought from Another Sweatshop Co., when it blows, shorts rather than breaks. Etc.
All this means, is that when you are adding your RAM, battery, new disk drive, etc. to your PC and you drop the battery, a screw, etc. there’s a short. Your MB is now junk. But you decide to retrieve that part. Now you’re reaching into a PC with a failed PS that isn’t supposed to have 120v coming out of it failed or good. But you don’t know about the crappy resistor which caused a short in a transformer and fried a diode that …
Leave it plugged in while removing the cover? The idiot who assembed your computer might have gotten a wire pinched between the cover and the case. The insulation was almost but not quite worn off. Removing the cover is just enough to break through the last bit of insulation. Poof. Assume that there’s a chain of errors. Don’t add the final link to the chain.
Plugged in but switched off? If I had a nickel something accidently got switched on when it wasn’t supposed to… . I consider any device I’m working on to have “plugged in = live”.
So why not just Be Safe???
I have an aunt that almost died because a radio next to the bathtub fell in while she was in it. No one “plans” on having the radio fall in. Everybody thinks “I’ll be careful, I won’t let it fall in.” And yet hundreds die each year because something unexpected happened and they get electrocuted. Electricity must be respected. It demands respect. The unexpected will happen no matter how smug you try to be.
Being smug is how you die.
Thank you for taking the time to explain all of that gazpacho and ftg. Good points and well made; I will not offer advice on this subject again.