it essentially does a stretched mirror around the lines y=1 and y=-1. Points in the range (0,1] get mapped to [1,∞) and vice versa. A good example of what it loos like it is comparing the graphs of sin(x) and 1/sin(x).

As for what functional purpose it has, it pretty much just lets you multiply the result in a calculation when you would normally need to divide by it.