title: When "dev-master" should be used in composer.json?
body: <p>I'm starting to use Symfony2 and following many tutorials. I found that when they installed some new features using <code>composer.json</code>, they "always" declared <code>dev-master</code>. I don't know the reasons why they always use it. An example from <a href="http://symfony.com/doc/current/bundles/DoctrineFixturesBundle/index.html" rel="noreferrer">DoctrineFixturesBundle</a>:</p>
  
  <pre><code>{
      "require": {
          "doctrine/doctrine-fixtures-bundle": "dev-master"
      }
  }
  </code></pre>
  
  <p>Actually, I have googled and found some people written that If we use the <code>dev-master</code> instead of any <code>stable</code> version. It would be some conflicts in the future because the version today maybe <code>1.5.0</code> and tomorrow maybe <code>1.6.0</code>. </p>
  
  <p>So, what we really use in practical works - <code>dev-master</code> or <code>specified version</code> and why? </p>