I started off designing PCBs using Eagle CADsoft and the tutorial series I watched showed how to create top/bottom GND planes on a board. All my boards have them, but I wonder if it makes sense to always have them. Is there a design rule which tells you when you should add one or both? In my latest board, there are only a handful of GNDs (highlighted in pic) - should I still add a GND plane? It does make routing harder sometimes.
