its the same as a jumper. sometimes a part of a circuit has to be bypassed for some reasons so we connect a jumper (0 ohm resister) in parallel with that part. an example of a jumper is the thing u use to set ur CD ROM/DVD ROM etc to Master, Slave or Cable Select.,,,,
It is used as a jump wire. Assembly manufacturing instruments are designed to handle components and not wires. So they make 0 ohm resistors to replace jump wires.
And another innovative use is to fox teachers who insist on zero jump wires in the circuit.
They're used on cheap (Radio Shack) PCB design a LOT in order to simplify PCB design by using cheap labor to solder the jumper wire in order to get a far simpler board layout. I have to my knowledge NEVER taken apart a device (cell phones or third party devices excluded) produced by Radio Shack that did not have multiple 'jumpers' AKA 0 ohm resistors.