Creating services in ENA allows you to understand your network from a service-based perspective, and not just from a component-based one. A component may go down but the overall service remains up, meaning you can more easily decide how and when to fix the issue.
You can also create service hierarchies by creating sub-services. The state of a sub-service contributes to the state of its parent service. This means you can model complex services with multiple contributing sub-services.