do you think it is taught

It was taught when I went through driver’s ed class in the US.

necessary

Yes. There’s an area in most vehicles that you can’t see from your mirrors alone, and if you don’t check it, you can hit a car there.

https://en.wikipedia.org/wiki/Vehicle_blind_spot

As one is driving an automobile, blind spots are the areas of the road that cannot be seen while looking forward or through either the rear-view or side mirrors (expecting that the side mirrors are properly adjusted on a passenger auto – see above). The most common are the rear quarter blind spots, areas towards the rear of the vehicle on both sides.

Some vehicles aren’t capable of letting you check those areas over your shoulder; they typically have parabolic mirrors or something like that to let you see the area from the mirrors. But the normal case is that you need to check to be driving safely.

EDIT: Now that I think about it, I’ve always called curved mirrors on vehicles and mounted at blind corners “parabolic”, and my parents always have as well, which I think is where I got it…but thinking it over now, I bet that they aren’t actually parabolic. There’s no reason for them to specifically follow a parabolic curve that I can think of; they aren’t dealing with trying to produce parallel beams of light the direction that the mirror is facing. They need to be curved, but not specifically parabolic.

kagis

Yeah, this doesn’t say anything about it being parabolic:

https://trafficmirror.com/stainless-steel-highway-traffic-mirrors/

And ditto here for a vehicle mirror. Just says “convex”:

https://www.amazon.com/RETRAC-610901-Stainless-Center-Mount-J-Bracket/dp/B08HVPGQ99