Postgres has a number of extensions which require superuser access for a user to install them, PostGIS being one of them. If you're wanting to install a GeoDjango app, you'll probably encounter an error such as:

$ ./manage.py migrate
Traceback (most recent call last):
  ..
django.db.utils.ProgrammingError: permission denied …

Although using Model.objects.create_or_update() with a Django model is extremely convenient, sometimes you might want to consider using it carefully with certain usage patterns.