James Cameron would like a word with you. Seriously though, 3D can show off some things that just might not be realized without it. Not sure of Fritzing's design abilities with layered PCBs, but I could imagine trying to design a layered board and forgetting how tall a component is. Seeing a component "through" the second layer could be useful
If your circuit is so complex that you need a breadboard planner and even an fully 3D visualization you have a big problem and you should not be breadboarding but ordering a PCB.
James Cameron would like a word with you. Seriously though, 3D can show off some things that just might not be realized without it. Not sure of Fritzing's design abilities with layered PCBs, but I could imagine trying to design a layered board and forgetting how tall a component is. Seeing a component "through" the second layer could be useful