My AD is in charge of watching blocking and making suggestions to me on the visual. I'm more a verbal director, and I know that visual is my weakness--so I really depend on AD's suggestions. I'll also use my AD to run lines with struggling actors or work scenes with them and help them develop their characters.
If we're really behind the rehearsal process, I'll have my AD hold one rehearsal in another room while I do one in the main hall (or vice versa). Of course, I have to make sure I have another adult present, so I usually call in favors of fellow faculty or offer bribes (show tickets and reserved seats) to get help.