What is the purpose of creating categories for contact labels? - Contact Security

https://docs.oracle.com/en/cloud/saas/marketing/eloqua-user/Help/ContactSecurity/Tasks/CreatingCategories.htm

There is information in the help center about creating and deleting categories for contact levels, but I would like to have a better understanding of what categories do in Eloqua and how they work. If labels can be directly assigned to security groups themselves, then what is the purpose of the categories?