Correct me if I am wrong, but what I think aj is trying to say is that he(?) would like to see a photosynth of his family but keep it private. Just like you can upload pictures to facebook and keep some of them private from others view. creating a family photosynth, akin to a old photo album, some things you just want your family to see.
Also private synths will allow for works that are still in progress and thus one can release a great brand new synth to the world that they have been privately refining for the last couple months. Something like that. Or one could start a small business utilizing the technology. You wouldn't want everyone to see what you were doing?