Why is a parallel circuit used in household wiring?
Parallel circuits are used in homes because the loads can be operated independently of each other. That means that you can have an electrical item turned on and running without needing to have all of the other loads on and running as well. A parallel circuit also allows all of the loads on a particular circuit to continue working even when one of those loads fails. For example, many homes have kitchens with 4-6 overhead "can" lights. They are wired in a parallel circuit to a single switch. If one of those light bulbs burns out, the other lights continue to work. If the lights were wired in series, all of the bulbs would turn off the moment one bulb burned out.
The other problem with a series circuit is that it divides the total voltage of the circuit by the number of loads on the circuit. More loads means less voltage per load. If the circuit contained only lights, the lights would get dimmer with the addition of more lights. A parallel circuit doesn't do that. Each load gets the full voltage of the circuit. That means everything on a parallel circuit is getting the full necessary voltage it was designed to get.