Comfort and Convenience
Preferred cabin temperature varies widely, and so does tolerance for air blowing directly at the face. Passengers sharing one setting often end up negotiating rather than agreeing.
Safety and Driver Assistance
Mirrors, seat position and the hazard switch are easier to sort out while stationary. Anything left until later becomes a task competing with traffic for your attention.
Multimedia and Connectivity
Taking a call with both hands on the wheel is different from holding the phone, and whether that is possible depends on the pairing or wiring available.