This article is goign to be bit of technical words, but I promise to keep it very simple & basic. It is important that you be aware of atleast this much of understand of how electricity flows inside your home & little about colour code inside Electrical Wiring.

Electrical Polarity (i.e. positive & negative) is present in every electrical circuit. The electrons flow from negative pole to positive pole. In DC (direct current) circuit, one pole is always negative, the other pole is always positive and the electrons flow in one direction only.

In an AC (alternating current) circuit the two poles alternate between negative and positive and the direction of the electron flow reverses.
Polarity is very important while doing the wiring for electrical equipment. Say the latest LED TV is installed in your home, these LED TV has AC & DC transformers but still the electrician need to match correct wires to create a correct circuit.

Wires come in RGB color mode i.e. red-green-black. The connections / wiring is done colorwise. When the wiring is being done and wire falls short for some reason, many electricians use another wire to complete the line. But this creates a joint, which is not good, safety-wise and consumption-wise. Joints in wiring increases the consumption of electricity. Wherever there are joints, the current get accumulated which is a total waste and there the consumption goes high.

Important : I would suggest all the home owners to spend a little more but have a single long wire for the wiring purpose rather than having joints. This helps you save on your electricity bill too. Say an electrician has given joints while doing the wiring for a room/house and days later the wiring has caught fire. Here the electrician will be caught coz I would happen only when the wiring isn’t done correctly. Also the power wires alternate in polarity & fluctuates in potential. Therefore positive and negative (the polarity) is necessary in circuit.