They have been used to route out copper from plated PCBs, cut out the part that etchant would normally remove.
That's a machining operation, not a 3d printing operation (subtractive vs. additive).
There's an outfit that makes a "PCB plotter" that is a desktop CNC mill for making PCBs. With all the optional accessories you get the capabilities to do plated through holes and double sided boards, but IIRC it was around US$20k for the whole kit.
-j