Kindly be informed that the PATH is an environment variable in Windows. It will inform the command line on which folders to look in when attempting to find a file. If you didn't add Python to PATH then you would call it from the command line like this:
C:/Python27/Python some_python_script.py
So, if you want to add it to PATH, you can perform this:
python some_python_script.py
It will work for you as the command line will look over all the PATH folders for python and find it in the folder that the Python installer has added there.