Airflow uses it for task ordering within a DAG, but that's used in the parsing step that happens before/outside of any actual task execution so it's not really in the source code of tasks at least.
The Airflow 2.0 TaskFlow API[1] doesn't use the bitshift operators any more -- if you pass the result of one task into another, the second task is automatically downstream of the first. So it all just looks like function calls, despite using XComArgs behind the scenes.
1. https://airflow.apache.org/docs/apache-airflow/stable/tutori...