title: What is the purpose of advertising a VOLUME in the Dockerfile if it can be omitted?
body: <p>I noticed by accident that it doesn't make a difference whether I advertise a VOLUME in the Dockerfile or not. (The Oracle database xe18.4 lacks the VOLUME statement) When I <code>docker run -v ...</code> the volume gets created without error.</p>
  <p>What's the purpose of advertising a VOLUME in the Dockerfile if it can be omitted just as well?</p>