Previs used to be a line item only large productions could justify. Generative tooling has moved it to somewhere near free, which changes what it is for: not proving the film can be made, but finding out which version of it is worth making.
The useful discipline is to previs the decisions rather than the shots. Two lighting approaches, three shot-size patterns, two performance registers. Comparing those is a real question. Comparing forty pretty frames is a mood board.
Previs frames are not plates and should never quietly become them. They are made fast and loose by design, and a previs frame promoted to a reference brings all of its sloppiness into the campaign.
Can previs frames be used as references for the final work?
Not directly. Previs is made fast and is not verified against anything. Promoting a previs frame to a reference imports every approximation in it into the finished set.
What should previs actually test?
Decisions with alternatives: lighting approach, shot-size rhythm, performance register. Frames without a competing version to compare against are decoration.