The motion starts much higher up. The part where your leg is up bumps their hip taking thier root (balance, then you lean on them with your elbows and drop straight down. You then shift forward to rol them on thier side. The back leg steps left into a horse stance and you anchor them in place as you china thier arm out of thier socket.
It's the posture inbetween the takedown, and the cage right before what could best be described as a standing arm bar.
That is one use for it anyway.
In systems that are used in mass fights, like riots or large gang fights where blunt and bladed weapons are involved it allows you to take an opponent down, without getting stuck on the ground yourself.
As a training tool, it trains the skeletal alignment needed to properly generate power on those angles.