title: Any valid reason for code duplication?
body: <p>I'm currently reviewing a very old C++ project and see lots of code duplication there.</p>
  
  <p>For example, there is a class with 5 MFC message handlers each holding 10 identical lines of code. Or there is a 5-line snippet for a very specific string transformation every here and there. Reducing code duplication is not a problem in these cases at all.</p>
  
  <p>But I have a strange feeling that I might be misunderstanding something and that there was originally a reason for this duplication.</p>
  
  <p>What could be a valid reason for duplicating code?</p>