It will basically provide safety protection from electrical shock. Occassional large electrical equipment may become temporarily energized --- maybe a down power line, or by accident. By grounding the equipment, the earth that you are standing on, and the equipment will always be at the same voltage. Therefore, even if the equipment becomes energized at 25000 Volts, the ground you are standing on will be at 25000 volts as well. So there is no potential difference and therefore, no electrical shock. Without the earth connection --- there would be a 25000 Volt potential difference, and you would suffer severe electrical shock, or even death. Excerpt from Wikipedia: Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment (the terms ground (North American practice) and earth (most other English-speaking countries) are used synonymously here). Normally a grounding conductor does not carry current. Neutral is a circuit conductor (that carries current in normal operation), which is connected to earth (or ground) generally at the service panel with the main disconnecting switch or breaker.
