Here in Australia we have what is called an MEN system. Multiple Earth Neutral, the IEC describes the MEN system as a TN-C-S system (Terra Neutral Combined Seperate) which is a fancy way of saying; the neutral and earth conductor are functionally and physically the same conductor between the star point of the distribution transformer and the point of supply, which will be at the consumer's property.
It is at the point of supply that the combined conductor seperates into two physical conductors, the neutral and earth. The main earthing terminal is then connected to the greater mass of the earth via the main earthing conductor and an earth stake. This process is repeated at every property and thus forms part of a system we call the PME system (Protective Multiple Earth) .
The reason the the PME system is straight forward, the further you get from the transformer the greater potential rises on the neutral conductor with respect to earth. The PME system allows the the voltage rise to disapate to earth at each property and thus keeps the neutral voltage consistantly low. By keeping the neutral voltage at as close to ground potential as possible affords use a good reference voltage and a means to mitigate voltage differences appearing between exposed conductive parts of equipment and extraneous conductive parts through equipotential bonding.
Having an earthing conductor allows for automatic disconnection of supply in the event of a short circuit to earth fault by fault current a low impedance path sufficient enough to operate the circuit protective device.
Fault current always wants to find its way back to the origin (the transformer).
So to answer your question; earthing is actually a very complex part of any distribution system and forms an integral part of the protection devices by allowing them to function as they have been designed to. The earthing conductor doesn't get enough credit for what it does!!!