Earthing

To protect a structure from lightning strike, directing the lightning through the earthing system and into the ground rod rather than passing through the structure.
As part of a single-wire earth return power and signal lines, such as were used for low wattage power delivery and for telegraph lines.
In radio, as a ground plane for large monopole antenna.
As ancillary voltage balance for other kinds of radio antennas, such as dipoles.
As the feed-point of a ground dipole antenna for VLF and ELF radio.

In mains powered equipment, exposed metal parts are connected to ground to prevent user contact with dangerous voltage when electrical insulation fails.
In electrical power distribution systems, a protective ground conductor is an essential part of the safety Earthing system.
Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices.
In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor.