The title says it all 
In what situation? At least Raytraced already displaces the groundplane with the tiniest amount.
Upon revisit it may have gotten lost in history… or not? Dunno, but no z-fighting for a plane on the ground plane. So ignore my rambling.
Pictureframe for modelling on groundplane:
Rendered mode:
Raytraced mode:
(Also notice how dark the pitcture frames are)
Hmm, the picture frames indeed show the z-fighting. Not sure why it doesn’t show with simple plaster plane. Consider it fixed in the next public WIP.
The darkness in the picture frame looks weird. Is that an image with a color designated as alpha?
the plane is just a picture plane, but it’s an older file. I’ll run some tests tomorrow.