The axle truss provides additional strength to the axle housing and the lower damper mounts.  This will be needed to deal with the additional cornering forces that the car will be encountering with these new suspension components.
photo of installed axle truss

One problem I encountered was the lower mounting hole for the right side damper was off by almost 1/4".  Apparently, the factory tolerances are quite tolerant.  A 1/2" drill opened up the hole in the axle bracket so that it lined up with the axle truss sufficiently to insert the mounting bolt.