Comfort and Convenience
Preferred cabin temperature differs from person to person, and passengers in the rear often feel it differently from the driver. Agreeing a setting early avoids constant adjustment during a drive.
Safety and Driver Assistance
Adjusting mirrors and seat position before moving, rather than at the first junction, is simply easier. The same applies to learning any unfamiliar switch on a recently acquired car.
Multimedia and Connectivity
Listening habits differ: some people want radio, others a stored playlist or podcasts from a phone. Which of these works depends on the sources the audio system supports. Calls and charging are separate questions.