A user account is an identity created for a single person to whom you want to give access to your Optable DCN. While it is possible to give access to a group (e.g. by inviting [email protected]) it is not recommended for security reasons. If you need to give access to a non-human/group for automated tasks, you should instead create a service account.
Service accounts are a special type of non-human account used to execute applications and run automated services, virtual machine instances, and other processes. An example of service account would be a script running in your cloud, automating a CLI export of an audience, or giving human-friendly name to audiences activated through GAM key-value pairs.