I see benefits to excessively civilized behavior in the first debate — let people know that Trump is not a crazy person.
I see benefits to excessively civilized behavior in the third debate — final impression should be that Trump is not a crazy person.
Bu the second debate — I suspect Trump can mix it up and score some dramatic points. Hillary might be surprised and/or it might throw her off later as she prepares for the third debate — will Trump attack? will Trump be presidential? She’ll have to guess. But I hope to see more fireworks at the Second Debate.
I used to have a choir director (may he rest in peace) who said that listeners tended to remember the beginning and end of a piece, the middle not so much.