What if the plumber missed a drain or supply by an inch? Guessing the robot doesn't adjust its outline. I.e. if a sewer stub is wrong by a few inches, the wall needs to be moved to fit the toilet, or the slab needs to be busted up and the sewer line relocated.
I suppose if it gets some of this wrong, it'll be obvious, and a human can correct it.
It's almost certainly not the layout guy's job to decide that the bathroom can be 3" larger than it was and the lobby 3" smaller.
I deal with this relatively often in a machining context - People complain that they'd rather just make simple parts on the Bridgeport manual mill rather than a CNC, because they can adjust on the fly with the manual mill but have to get the CAD changed so that CAM can adapt to the modifications. But when they make it manually, and a year later we need to ship out a replacement part or develop an ECO... if you did it by updating the CAD then the replacement part will fit. If you just freehanded it, the part will not fit.