Should I constantly use Django select_related and prefetch_related?

Question

Should I constantly use Django select_related or prefetch_related every time when I use models with OneToMany relations?

If I have multiple foreign keys. Can I use it, like this?

class A(models.Model):
   pass

class B(models.Model):
   pass

class C(models.Model):
   a = models.ForeignKey(A)
   b = models.ForeignKey(B)

# example usage
for entry in C.objects.all().select_related('a').select_related('b'):
   pass

Answer 1

You could also use it like this:

for entry in C.objects.select_related('a', 'b').all():
   pass

And you should use it only when you want to get the foreign keys to make operations with them in another case you shouldn't.