Something I did not know, but when I found it on this post, then I just realized that is include somewhere in PHP manual, so I quote from original manual entry.
“If called from the global scope, then execution of the current script file is ended. If the current script file was include()-ed or require()-ed, then control is passed back to the calling file. Furthermore, if the current script file was include()-ed, then the value given to return() will be returned as the value of the include() call. If return() is called from within the main script file, then script execution ends.”