Rowing using your body weight to help your drive is a difficult skill to have but a very good way to go fast and row efficient. To do this well you need to have very good coordination and good body strengths. Rowing for me is a balance of rhythm and power. The power needed in rowing is the one that moves the boat and the rhythm is the reaction of this power and the body weight used well in coordination with the boat. In this first picture you can see this 2x holding to the finish when their body weight is still up. You can see how engaged is their upper body to keep that body weight up and how low is the water line on the boat. The water line is lower and you can see more boat because the bodies are not dead on top of the boat but hanging on the blade.
In this next picture you can see that the rowers have dropped their body weight and the water line is covering more boat.