Question about Game of Thrones directors

Directors, whether they be in movies or television, heavily rely on their second unit director. In a series as complex and as spread out as Game of Thrones, you probably have a third and maybe even a fourth unit director who help oversee production. A director can't be in two places at one time. So these secondary directors stand in in place of the director and film scenes accordingly. However, they conform to the standards and criteria set forth by the episode's primary director. In the end...it is the primary director's vision.