A superconductor!
But seriously, I use them in places where I have a spot on a circuit
board, and, due to a reconfiguration, I need a short instead. They
are also used when a design might be changed in production. If
your autoinsert machine is already set up for placing chip resistors,
then it's easier and cheaper to just throw in a roll of zero ohms
instead of doing a board redesign, or trying to place jumper wires.
Same goes for '1/4' watt resistors. I have a bunch with just a black
band around them. Epoxy encapsulated wire!
In addition to what was mentioned by the other folks, here is a different purpose for them. Zero ohm jumpers are just that, jumpers. For example, when you have a layout for a PC board that is single-sided (cheaper than double-sided) and the circuit requires two or more traces to cross but it is physically inpossible for them to do so on the copper side of the board, a zero-ohm jumper will traverse traces that cannot otherwise be crossed to make a required connection. You might use pieces of bare or insulated wire cut to size, but with automatic insertion machinery, it is far easier and less labor-intensive, not to mention less time-consuming and costly than making the jumpers. Although there are machines that can quickly strip, cut and bend wire, you would not need to buy one because it is easier for the sequencer to just stick something shaped like a 1/4 watt resistor in the sequenced parts or if surface mount, to take a standard size and shape to pick and place from a reel of them to perform the same function. I hope this helps without confusing you.
Thank all of you for your responces!
Makes sense now. Our confusion at work was why a 0 Ohm resitor vise a simple jumper. Now makes sense, logical I might add as to why.
Thanks very much again for your responces!
