Why use UniqueTogetherValidator over Django's default validation behavior?

I have a Django model defined with a unique_together relationship defined between name and address, shown below:

class Person(models.Model):
    name = models.CharField(max_length=255, default='', null=False)
    address = models.CharField(max_length=255, default='', null=False)

    class Meta:
        unique_together = ('name', 'address')

I also have a Django REST Framework serializer with a UniqueTogetherValidator describing the same constraint as defined in the model, shown below:

class PersonSerializer(serializers.ModelSerializer):

    class Meta:
        model = Person
        fields = (
            'name', 'address',
        )
        validators = [
            UniqueTogetherValidator(
                queryset=Branch.objects.all(),
                fields=['name', 'address']
            )
        ]

While testing this constraint, I noticed that the exact same behavior is exhibited whether or not I have the UniqueTogetherValidator added to the PersonSerializer. The same error message is returned whether or not I include this (due to the unique_together defined on the model).

My question is: what is the reason for explicitly declaring validators on the serializer if the behavior is performed behind the scenes? I did notice you can change the error message, but this seems like quite a bit of boilerplate for solely manipulating an error message for violating a unique_together constraint. Is there a broader reason for utilizing these validator classes that I'm missing?