What i mean is when you have a 3 phase net you get get 380V between the line voltages and 220V between neutral and line (when you have a 220/380V grid),if someone switches the neutral wire with a line wire you will get 380V instead of 220V on one of the connections.
Also a bad connection in the neutral wire can cause voltage fluctuations between line and neutral where depending on the load one phase can have 180V and on another you can get 260V or more.This happends a lot.Now the undervoltage won't hurt anything but the overvoltage ...
Now on the other hand,let's say you have an open air gig and everything has to be build from scratch it's not unlikely that a mixup in the wiring can happen,have seen it before.
This is the reason i bought a furman power conditioner series II,these don't work with VDR's anymore but they have an active sensing circuit that measures the incomming voltage,and if it's too high it will go into protect mode and won't switch on the outputs that go to your gear.I find this a lot safer then the VDR's where you will have to hope that the internal fuse will blow on time when the VDR protection comes in.But usually this is not case.And afterwards you need to replace all the VDR's in the PC.And they blow a lot,have replaced these a lot back in the days.
So it's not only EMI/RFI suppression that is important but also the level of protection.So it's better to invest 200 euro in a good device that protects your gear then paying a lot more when something goes wrong at a gig or even at your home.
Furman is the world leader when it comes to PC's.They are not cheap but they are just the best you can get.