Use case of dummy operator in Apache Airflow

Operator that does literally nothing. It can be used to group tasks in
a DAG.

https://airflow.apache.org/_api/airflow/operators/dummy_operator/index.html

As far as I know, at least two use case:

• test purpose: in DAGs, the dummy operation is just between upstream and
  downstream, later, you can replace the true operator.
• Workflow purpose: BranchPythonOperator works with DummyOperator. If you want to skip some tasks, keep in mind that you can’t have an
  empty path, if so make a dummy task.
  https://airflow.apache.org/concepts.html#workflows