The subject is package imports and the __init__ file:
There is one quote in the specification that says

these files serve to prevent directories with common names from
  unintentionally hiding true modules that appear later on the module
  search path. Without this safeguard, Python might pick a directory
  that has nothing to do with your code, just because it appears nested
  in an earlier directory on the search path.

Can you give me practical examples of this ?
If you allow any directory to be seen as a package, then trying to import a module that exists both as a directory and as a module on the search path could pick the directory over the module.
Say you have a images directory and an images.py module. import images would find the images directory if it was found earlier on the search path.
By requiring a __init__.py to mark packages you make it possible to include such data directories next to your Python code without having to worry about masking genuine modules with the same name.
Hide true modules