title: Disadvantages of shallow cloning on Travis and other CI services?
body: <p>Most CI services provide a way to shallow clone a repository. For example, on Travis:</p>
  
  <pre><code>git:
    depth: 1
  </code></pre>
  
  <p>or on AppVeyor:</p>
  
  <pre><code>clone_depth: 1
  or
  shallow_clone: true
  </code></pre>
  
  <p>This has the obvious benefit of speed, since you don't have to clone the whole repository. </p>
  
  <p>Is there any disadvantages to shallow cloning on CI services? Is there any situation where a shallow clone would make a CI build fail? Otherwise, why isn't shallow cloning the default setting for these CI services?</p>