title: What is the reason for the /a /b prefixes of git diff
body: <p>I've been using Git for some years now and always wondered why <code>git diff</code> prefixes the names of modified files with <code>a/</code> and <code>b/</code>. I expected to eventually stumble upon a use-case where it is useful, but until now it was always annoying and never helpful.</p>
  <p>What is it good for? Why is this enabled by default? In which situations is it useful?</p>