It is NOt the 3D visualisation that is important . That is only eye-candy and serves no purpose.
It is the capability of the program to check spatial positionin gin 3D that is important. Verifiying that no components will touch each other , touch the case, wanted or unwanted. Combine that with interaction capability with mechaincal world : loading the case for example, and exporting the pcb , with components, in a machine readable 3d format so the alignment of connectors in the case will be right. The lightpipe will mate with the led on the board etc .
3D is only usefull if you can actually EDIT in 3d mode. : meaning you can position parts while in 3d view. And the program tells you on the fly if you have collisions or not. Begin able to generate a synthtic image through a renderer is pretty much useless and only good for showing a picture.
the real power lies in the interation with the mechanical world.
Very advanced programs allow you to design flxible or rigid-flex boards , where you can actually bend the flex to check the end result will work correctly. I did a little board that has three flex sections , two have a pushbutton , the third a pushbutton and an antenna. This thing mates with a plastic base shell that has a battery holding clip. And then there is an outer shell that encapsulates this whole construction. The end result looks like a little car. You can push the nose, trunk , roof , and side doors. due to the very small form factor ( the size of a 'matchbox' car ) this board needed rigid-flex. everything snaps together with clips molded in the plastic pieces ( no screws ). The mechanical people designed the body shells , i extracted usable space for parts , can figure out what part can go where , folded the board , sent back the pacb design and the created the internal support structure for my board.
we sent the cad data to a 3d printer that printed the outer shell, the inner structure and a 3d model of the pcb including parts. everything fit perfect on the first try. so we ordered the dies for the plastic injection molding and the pcb's.
That is why 3D is necessary in PCB design. Getting things first time right. just 'darwing interconnections on a plane is not board ' design'. it is only a subpart of the entire design cycle.
Designing a board is everythign from schematic capture, simulation o the schematic, part placement, board material selection , assembly techniques , soldering tecniques, multilayers, blind and buried, laser vias, flex , downt checkign the routing for parasitics, cross coupling , impedance, termination and making sure the mounting holes are in and the damn thing fits the box it needs to go in to.
3D editing and realtime visualisation is a big help in certain of these area's. It speed sup the process and eliminates errors.
Couple that with file exchange of 3d models and you have a big advantage in both time and reduction of possible mistakes
Offline rendering ( non realtime) is only good for eye-candy. And i will be the first to just shrug at tools that do this offline eyecandy stuff through a renderer. that is useless. (apart for marketing purposes)