title: git pull --rebase --preserve-merges
body: <p>Short version:
  Do you need to preserve-merges only if you explicitly merged after you did a local commit? What exactly happens otherwise? Does it reapply your committed code to the merged branch?</p>
  
  <p>Please explain when it is useful to <code>git pull --rebase --preserve-merges</code> vs. a regular <code>git pull --rebase</code>?
  I read about an issue with <code>git pull --rebase</code> here:
  <a href="http://notes.envato.com/developers/rebasing-merge-commits-in-git/" rel="noreferrer">http://notes.envato.com/developers/rebasing-merge-commits-in-git/</a>
  That could cause code changes to be duplicated.</p>
  
  <p>I read here: <a href="https://stackoverflow.com/questions/2590260/when-will-git-pull-rebase-get-me-in-to-trouble">When will `git pull --rebase` get me in to trouble?</a></p>
  
  <p>That it only happens if you basically rebase after some the commits have been pushed.</p>
  
  <p>So I am not sure I understand when I would need <code>git pull --rebase --preserve-merges</code> and if it's ever bad to use vs.  <code>git pull --rebase</code>.</p>