Usually we’d open a car door from the inside using the hand nearest the door, but this isn’t the best way to see into the blind spot that’s created by the B-pillar just behind your head. This can mean that you miss difficult-to-see road users like cyclists, and end up opening your car door in front of them.
You get a much better view if you turn your whole body to the rear rather than just your head. If you open the door using your opposite hand (i.e. the hand further away from the door) it forces you to turn your whole body. This is called the Dutch Reach and it’s encouraged in Holland (for the last five decades), the UK and other countries as a safer way to open the door.
For passengers exiting the car, it’s safer for people using the footpath.
Of course, you also check the mirror before you exit to give yourself the best chance of seeing something coming from behind.
The best view is given by opening the door slightly and taking another look, then opening it carefully, especially if your door forms part of the B-pillar, because this will make the B-pillar effectively smaller.
The only time the Dutch Reach is not desirable is if the driver or passenger have mobility issues that prevent them from doing it. Morbid obesity, pregnancy, a bad back and shoulder injuries are some of the reasons it might be impossible or, at the least, not comfortable, to open the door using the Dutch Reach technique.