title: Why is it recommended against using a dynamic start_date in Airflow?
body: <p>I've read Airflow's FAQ about <a href="https://airflow.incubator.apache.org/faq.html#what-s-the-deal-with-start-date" rel="noreferrer">"What's the deal with <code>start_date</code>?"</a>, but it still isn't clear to me why it is recommended against using dynamic <code>start_date</code>.</p>
  
  <p>To my understanding, a DAG's <code>execution_date</code> is determined by the minimum <code>start_date</code> between all of the DAG's tasks, and subsequent DAG Runs are ran at the latest <code>execution_date</code> + <code>schedule_interval</code>.</p>
  
  <p>If I set my DAG's <code>default_args</code> <code>start_date</code> to be for, say, yesterday at <code>20:00:00</code>, with a <code>schedule_interval</code> of 1 day, how would that break or confuse the scheduler, if at all? If I understand correctly, the scheduler would trigger the DAG with an <code>execution_date</code> of yesterday at <code>20:00:00</code>, and the next DAG Run would be scheduled for today at <code>20:00:00</code>.</p>
  
  <p>Is there some concept that I'm missing?</p>