I have only had two experiences team teaching (the pairing up of a Japanese teacher with a foreign teacher in the same classroom.)
The first time was when I first came to Japan 17 years ago as a new English teacher. I thought the experience was for my benefit, to help me learn how to teach. It was a very pleasant experience because I had no idea what the Japanese teacher was saying.
My second experience team teaching was more recent, at a private junior high school. This time, I thought the purpose of team teaching was to assist Japanese teachers in teaching proper English pronunciation. But when I asked why team teaching was required for Japanese first-year junior high school classes, they said the purpose was to help the students make the transition from having a Japanese teacher to having a foreigner teacher. Hmmm.