title: pep 420 namespace_packages purpose in setup.py
body: <p>What is the purpose of the <strong>namespace_packages</strong> argument in setup.py when working with PEP420 namespace packages (the ones without __init__.py)?</p>
  
  <p>I played with it and saw <strong>no difference</strong> whether I declared the namespace packages or not.
  "setup.py install" and "pip install ." worked in any case.</p>
  
  <p>I am building an automatic setup.py code generator and would be happy not to handle this if this is not necessary.</p>