Comfort and Convenience
Some drivers want air aimed at the face, others at the feet or windscreen. Preferences follow the weather outside, what a person is wearing and simple habit, so passengers often ask for different settings than the driver.
Safety and Driver Assistance
Preparation is easier standing still. Adjusting the seating position and mirrors, then checking which stalk works the indicators and which the wipers, means those actions need no thought once traffic demands attention.
Multimedia and Connectivity
Taking a call without handling the phone is a different task from playing music. Where such a function exists, it usually needs setting up in advance rather than during a journey.