title: Airflow + celery or dask. For what, when?
body: <p>I read in the official Airflow documentation <a href="https://airflow.apache.org/configuration.html#scaling-out-with-celery" rel="noreferrer">the following</a>:</p>
  
  <p><a href="https://i.stack.imgur.com/BeHip.png" rel="noreferrer"><img src="https://i.stack.imgur.com/BeHip.png" alt="enter image description here"></a></p>
  
  <p>What does this mean exactly? What do the authors mean by scaling out? That is, <strong>when</strong> is it <strong>not</strong> enough to use Airflow or when would anyone use Airflow in combination with something like Celery? (same for <code>dask</code>)</p>