Its rare in TV animation these days for the director to be in the same location as the animators. On Monster By Mistake, we were lucky to do the first 26 episodes entirely under one roof. For the second 26, I was able to keep the animation local, though the modeling and lighting were done elsewhere.
When working with a group of animators, a director soon learns their strengths and weaknesses. Some are better at dialogue than action. Others are better at comedy than emotion. Ideally, each sequence should have a reason for being in a show and the directors job, through casting animators, is to put that reason across to the audience as strongly as possible.
There are live action directors who claim that casting is the most important part of their job. If you get the right performers for a role, youve solved most of your problems. Sadly, in TV animation, casting the animators isnt seen as a priority. Usually, when an animator needs more work, the animator is just handed whatever is ready to go.