As a rule the notion of a short circuit has a negative meaning since for real life devices a short circuit can be unwanted or even dangerous.
A short circuit is an electric connection of two points in a circuit with various voltage values not provided for by the structure of the device and disturbing its normal operation.
A short circuit appears as the result of broken insulation of current-carrying components or due to mechanical touching of non-insulated components. During a short circuit the intensity of the current running through the circuit soars. This produces considerable amounts of heat. As the result the device or electric wires may be damaged by the heat. This may even cause a fire.
A short circuit within one component of a power system can disrupt its operation in general. Other consumers may experience power supply voltage drops. Asymmetrical voltages appear in three-phase circuits in case of short circuits. This disrupts the normal electricity supply. A short circuit in large power grids may cause serious system breakdowns.
In case aerial line wires are damaged and earthed in the ambient space a strong electromagnetic field may appear. It can induce electromotive force in the nearby electric equipment. This is dangerous for the equipment as well as for the people working with it. Near the location of the breakdown voltage is spreading over the surface of the ground. As the result step voltage may reach a value dangerous for humans.
You can protect yourself from a short circuit, if you use step-down transformers with low-voltage split winding and fast-operating switching units with short circuit current restriction function. You can also use relay protection devices for cutting off the damaged sections of the circuit.