Well,
Parallel circuits are circuits that have only one "line" running through all the appliances in the circuit.
A parallel circuit can be more advantageous to a series circuit because you do not have to use as much wire.
However, the fact that the current must run through every appliance could be a problem. The most common is when an appliance (say a light bulb) wears out or breaks.
There is no longer a complete connection, and we now have an open circuit.
The parallel circuit I find the most annoying is Christmas Tree lights, where when one light bulb goes bad, all the other bulbs in that line go out.
