Earthing Principle and advantages

Earthing principles:

In electrical systems, an earthing system or grounding system is circuitry which connects parts of the electric circuit with the ground 

Earthing is a complicated  subject in safety of most electrical installations however there are three main points to be made. 

1) The earthing connections must be sufficiently robust andconductive to allow sufficient current to pass safely in
order to operate overcurrent or other protective devices
promptly, including those for earth-leakage protection.
Protective devices must be suitably rated for the fault
currents which might be expected.

2) It prevents the outer conductive casing of apparatus and conductors from assuming a potential which is dangerously different from the surroundings for any appreciable length of time although if a fault does occur inside the equipment the outer casing may actually be raised to a dangerous potential momentarily
3)Care must be taken against the occurrence of dangerous earth-potential gradients due to fault currents flowing in the terminations made to the general mass of earth. The`resistance areas' of the earth electrodes of different systems should not be permitted to overlap to any significant degree. The purpose of this is to prevent faults on one system imposing dangerous voltages onto the protective (earthing) conductors of other systems.
 
4)Earthing is also used for functional purposes, for signalling and draining leakage currents. The needs of these uses can sometimes conflict with the safety objectives of earthing.

references:  Laughton, M A; Say, M G (2013). Electrical Engineer's Reference Book. Elsevier. p. 32. ISBN 9781483102634.