Just about everything we can recognize have layers on the surfaces. For instance. Looking at the sun. Different layers. From this I guess that plasma layers could enable much smaller fusion devices.
So I guess that there exist an abstract reason for layers and why we should use them. Some clues might come from machine learning and its outer and inner layers.
One idea I had before was to use machine learning for batteries. Maybe there exist two outer and one hidden layer for the respective electrode? Maybe the rearrangement of the ions are complex and it could best be solved or iterated by a deep layer electrode.