In quite a lot of PCBs that I have seen, they often have these small metal bars going across from one point to another. 

Here is an image of what I am talking about. In this example it is a charger: 

J2 and J3 are what I am talking about

For reference, here is the other side of the PCB:

So, 


What are these called? 
What is the point of these? Why not just use tracers in the board or a wire?


These are called "jumpers" or "jumper wires" and simply connect two parts of the PCB together. They are common for single-sided PCBs to make a connection that may not be routable. The alternative would be to have a double-sided PCB, but that would be more expensive.