Should I turn off my PC when plug/unplug external display? Some people don't do that, but I think this is required to keep safe your equipment. Am I correct in thinking this?
Rationalization / Support
Areas of possible concern
Closing Thoughts (Almost)
When trying to answer the question "Should I....", it becomes a calculated risk (as any real world problem is). Take a moment to answer these questions and it should give you your answer. There can be many more variables to the calculation, but this should at least get the point across.
Business Environment Variables
Do you see where this is going? By powering down and back up each time you want to move your machine several times / day it could quickly become evident that buying a new machine + display would be cheaper in the long run. Please note that if you switch a lot during a meeting with a number of employees, the cost per minute skyrockets.
Consult the owner's/operator's manual of the display device. Most likely the manual states that both display and PC should be powered off when connecting them. Obviously this would be the safest and no-risk method.
The capability of connecting devices while one is powered on (aka hot-plugging) is partly determined by the connector design. If the electrical ground connection(s) cannot be established before any power and then signal lines are connected then there would be the chance of damage to line receivers. Inspect a USB device connector and you'll see that the contacts are not all of the same length; note that USB devices are hot-pluggable.
Neither VGA (HD-15) or DVI connectors are designed for making ground before signal, so there could be some risk when connecting powered devices. Just because someone has done it without problems does not mean that you never will. BTW I've seen electricians work on live circuits, i.e. they don't shut power off to replace a outlet; just because it can be done does not mean it should be recommended to others.
I kept plugging my HP dv5 to an external monitor while both on for a while till one day all of the sudden as soon as I plugged in VGA to the laptop, the laptop went blank. The monitor was fine but the laptop's either main or video processor went out.
The risk of hot swapping is too high. From now on I prefer to lose 2 - 3 minutes rather than the laptop.
Years ago, we had a DataTrain monitor that was misbehaving.
In a fit of frustration i unplugged, plugged in, unplugged, plugged in, unplugged, plugged in, ... the monitor cable from the video card.
The monitor never worked again.
So i don't do that anymore.