With liquid cooling you are cooling just one side, why not the other one as well EK must have figured. They have the first proper active backplate cooling solution that is integrated seamlessly, in a way that doesn’t require awkward soft tubing connections.
Since the PCB itself is basically a huge heatsink – it has several layers of copper that make up all electrical traces – it is great at absorbing heat from all of the components on the PCB. Removing excess heat from the PCB will lower the overall temperature of all the components on it, even those that are not directly cooled. With the newest power-hungry GPUs that have their components densely packed, every additional cooling is very welcome since lower temperatures also allow higher overclocks and more GPU boost. And with flagship graphics cards, like the RTX 3090 that has video memory placed on the PCB’s backside, it makes even more sense to use additional cooling.
Another thing is the benefit of thermal pads between the PCB and the backplate since it reduces coil whine. Thermal pads act as absorbers – they are soft and could lessen the coil whine caused by the vibration of the inductor coils. Having a small water block on the backside of the GPU makes the whole assembly sturdier compared to only having a standard backplate, which in turn acts as a better absorber of vibrations.