It goes on the front of the control arms and it ties them together (they are kind of jutting out into space). When you go into say a right hand turn, most of your weight is shifted to the front left tire. This means that the chassis will twist/bend the most (yes its not completely rigid) at that corner. By tying it the other control arm you reduce this bending and this keeps your tires planted on the ground better as you go through the corner.
Subachad was the first to make/put one of these on his car. He was doing autocross at the time and was looking for better handling. Here is a quote from when he installed his:
Originally Posted by subachad