Why are some principal characters missing from some TV episodes?
What's even more difficult to understand is when they're even included in a few minutes of the episode, and then they are written out of it. That would seem to imply it wasn't an emergency- or health-related issue on the part of the actor. It would seem to imply that it's a structured way to save money. But even this doesn't quite make sense for the average million dollar TV series.
Just as an example, in the 3rd season of House M.D., in the sixth episode (the one featuring an overweight man), the story includes Dr. Chase for a few minutes. Then, he seems to be written out of the episode for no known reason. He's a principal character, so it seems strange.
For what reasons might this happen?