When it comes time to go into dress rehearsals, know that this part of the production process will be the last opportunities to iron out any kinks in the show before opening night. And because these are the last chances to catch anything, the rehearsals will run as though as though it was the real thing — quiet backstage, hang out in the green room during breaks, and listen for cues for scene changes or to go on stage.
This will also be the point when the stage manager will be running the booth as though it was the real deal, with the assistant stage manager running the wings and yelling at the actors backstage. The director would be an observer for the most part — primarily running actors through warmups beforehand and giving feedback on the show afterwards — with no possibility of interjecting during the “show”.
These dress rehearsals are the last rehearsals that the director will be here to help the cast and crew, meaning that these last rehearsals will resulting in the “shift of power” between the director and the stage manager. Note that this does not mean that the stage manager will automatically trump the director in any situation, however this does mean that the stage manager has a lot more power at this point than at the beginning of the production.