Save "partial file" when saving local copy?

The instructions page for saving a local copy does not mention this anywhere. But I’m wondering what “save partial file” actually does. I had always assumed that it would at least save the variables, but not any image assets. But I would like confirmation on this. Sometimes I clone a file just for the variables (dont need all the other stuff in it) and I use “save partial file” to do this quickly. Is this a safe assumption or??