This mechanism provides more rectilinear movement of the rear axle of the vehicle in the vertical direction, prevents horizontal movement of the beam relative to the body which improves handling and control of the vehicle.
How it works:
https://www.youtube.com/watch?time_continue=1&v=a8cJCqWkfgk
https://www.youtube.com/watch?v=-J4xkHuP7QY
VAZ 2101 21011 21013 2102 2103 2104 2105 2106 2107 RIVA 2121 21213 21214 2131 2123 Chevy NIVA 4x4
 
VAZ 2101 21011 21013 2102 2103 2104 2105 2106 2107 RIVA NOVA LAIKA
2121 21213 21214 2131 NIVA 4x4