What does adding POSTGRES env variables achieve? Django + Postgres DB

As I have a Django App (using the app platform) with a connected DB, the connection to the DB seems to work out of the box. However, some tutorials online suggest I add the following env variables to my app:

POSTGRES_DB = ${db.DATABASE}
POSTGRES_HOST = ${db.HOSTNAME}
POSTGRES_USER = ${db.USERNAME}
POSTGRES_PASSWORD = ${db.PASSWORD}
POSTGRES_PORT = ${db.PORT}

And also some associated code in my settings.py file.

I wonder - what will this achieve? :-)

Best regards Frederik