Difference between 14nm and 7nm GPU

Many GPU vendors are moving towards smaller and smaller gpu package size. AMD and Nvidia have 14nm gpu's. They are working on 7 nm gpu now.

What makes it better to move from 14nm to 7nm ?
Smaller the package, lesser the power consumption on the GPU. So they can pack more transistor onto the gpu wafer physical size. That means essentially, AMD or Nvidia GPU is not going to consume lesser power. They would most likely consume same power by packing more transistors and giving better performance on the same physical size.