Why is the rehearsal so important?
Answer from a Native speaker
The rehearsal is important because they need to know what to do when they're actually shooting the scene so as to not waste time or get anything wrong, especially with stunts like levitating. It means they'll be fully prepared when they shoot the scene. I assume getting all the cameras to the site, and renting it, would mean they have a time limit.
1/2 STEP LEARN