Other than text, this is what most users will be adding to his post. Unlike all of us, many users will look at 'Upload a File' and not realize that they can easily upload a photo through the button. The image and video button are also very small on most modern resolution sizes and will not be noticed by users. That's why adding something they can't miss will be extremely user friendly.
If users can type text and add a photo/video, the basic functions of a post will be complete.