Comfort and Convenience
Cabin temperature is a preference people rarely agree on. Build, clothing and how long someone has been sitting still all change what feels pleasant, which is why the same setting can suit one occupant and feel wrong to the person beside them.
Safety and Driver Assistance
Time spent before setting off, finding the hazard switch, the demister and the mirror controls while still parked, means fewer decisions are left until the car is moving. Preparation of that kind is simply easier done stationary, when nothing else competes for attention.