Let me assume that the cameras are used to register with the edges of the material. In theory, if the edges of the material are cut true vertical 90 degrees than we can assume that the bottom surface of the material is the same dimensions as the top surface of the material and then we will have accuracy as fine as a human hair when flipping the material over for the second pass. that would be nice because you wouldn’t see any step when looking at the cut edges.
At the same time, I see that the top camera in the lid is fixed in the center (which I assume is the only camera, wide angle, that can see the entire material in view but not the side edges of the material)
So, if I purchase material from Home Depot or any place other than Glowforge, and I cut on my table saw to fit on the laser bed, I would have to make sure that my saw blade is 90 degrees vertical and not tilted in any way. otherwise, I think I would expect the laser cuts on the flip side to be off by as much as my vertical edges are not true.
That does not mean that Glowforge cannot do it. Maybe there is a way that the engineers have the lower camera attached to the laser head travel the outside edges of the material prior to cutting so it knows if it will need to compensate when flipped. At any rate, I will be thrilled to see a demo of this feature in action!