As far as I know, the CDF can be used to distribute projects in which you can interactively evaluate the projects without need to have Mathematica.
Recently I notice that the files in the Demonstration Project contain CDF files in which the code is not at all included. If you check this Radial Engine example and download the CDF file you will see that the code is not anywhere in the file and to get the code you have to download it separately.
How can that be done? Is it just simply delete the input cell and keep the output cell and then export the file as standalone CDF or something else has to be done.