Josh has given the answer ABOVE. If a COMPUTER Coordinator becomes a HC elsewhere. Not you...
-- Chemistry helps makes your players happier and less likely to complain to the media or retire early.
-- Strategy does nothing when you are playing the actual game calling the plays in a game you are playing, if you sim and selected the head coach to call the plays then it makes your sim play calling better.
-- Play calling again does NOTHING if you are playing the actual game and calling the plays. It comes in to effect if you sim the games and you selected the head coach to call the plays.
-- Performance makes everyone on the team a bit better. Since all player report to you and their individual coaches.
All of these were asked and answered before... nobody is guessing.