Ok here's the problem.

Nobody knows that the take is bad til it is shot. It's not til you are watching the cut that you realize it. You never do a spitscreen if the take is perfect. The director says while in post production,

"Wow I'd love to use her from take 3 and him from take 13".

This never happens on the day. Ok maybe it does but not in this capacity. The only planned spilt screens I have done are explosions or animal comps.

This is why they call it fix it in post. If you knew the talent was going to screw it up. You would just do another take. If you want to impress me do it to shots already shot and need fixing. Also notice that most of the shots they are demoing are lock offs. Not a good sign.

The Foundry has had a tool called Rig Removal for years. It has worked 3 times. Those 3 times required a huge amount of clean up.

Love the name.