I Germany this is taught as 'Schulterblick' ('over the shoulder look') in driving school (which is mandatory in this country).
In general, you are taught to always use Schulterblick when:
1. Changing lanes.
2. Entering/exiting from/to a ramp.
3. Turning.
4. Getting out of a parking spot.
5. Opening a door to exit the car.
Modern rear mirrors are curved at the outer vertical edge to avoid any dead spot.
This means just checking the mirror before you do any of the above should -- in theory --, be enough (except for some cases of 3).
But better safe than sorry.
An exception are trucks. They have a dead spot at the right which the driver can't check. Mercedes introduced a an electronic solution for this in 2014.
In general, you are taught to always use Schulterblick when:
1. Changing lanes.
2. Entering/exiting from/to a ramp.
3. Turning.
4. Getting out of a parking spot.
5. Opening a door to exit the car.
Modern rear mirrors are curved at the outer vertical edge to avoid any dead spot. This means just checking the mirror before you do any of the above should -- in theory --, be enough (except for some cases of 3).
But better safe than sorry.
An exception are trucks. They have a dead spot at the right which the driver can't check. Mercedes introduced a an electronic solution for this in 2014.