What would you capture in a clean plate before striking a setup?

[john2035]

I'm trying to understand what should be captured on set if an empty version of a shot might be needed later. This is a planning question, not a problem from a completed shoot.
Imagine a locked shot of an adult standing beside a window. There is a chance the person will need to be removed in post, but that decision hasn't been made when the setup is ready to strike.
Would you normally record an empty take immediately, with the camera and lighting untouched? Beyond matching framing, focus, exposure and white balance, what do you check before deciding that the plate is actually useful?
I'm particularly unsure about the person's contribution to the image. If they cast a shadow or appear in a reflection, is the empty take enough, or would you want additional coverage of those areas? How do you handle daylight changing between the performance and the empty take?
Finally, how do you decide how long to hold the empty frame when there are moving curtains or changing reflections? I'm not assuming a frozen frame or generated fill would replace captured background. I'd like to know which small omissions most often make a clean plate difficult to use later.

 

[David Jimerson]

That's really a decision which should have been made before you even set up.

As for a clean plate, like room tone, I'd generally suggest shooting it for the length of the scene. That goes against some conventional wisdom, but if you only have, say, 30 seconds, you only have 30 seconds.