Use of zero ohm resistor in pcb design
The zero ohm resistor is simply a jumper that can be conveniently populated with pick and place machinery.  Sometimes the board is too tight to route without crossing sides a zillion times, and a simple jumper can really make the routing much nicer.  Other times, you might want very tight control, making sure that two ground planes, for example, touch at only one point.  A jumper can make this simple and apparent.  The resistor is simply a jumper that can be machine handled.