What is wire labeling?
Why should we use them?  

What is wire labeling?

Wire marking is when you label, or mark, all wires with information like where is it coming from and where to go.

Why should we use them?  

When wires are not labeled, people working on them can accidentally cut or unplug the wrong wires, which can be very dangerous.
For example, If someone disconnects the wrong wire and the wire that was supposed to be cut is still in the connection and there is some work going on at the other end, he can get electrocuted.
That’s why we should always label each wire.