Retaining control is a positive because it allows you to change your mind and change what's being done with the data--or for that matter for legislation to limit wat you may do with the data.

Once the data is out of your control, there is no longer any way to control what is done with it. Don't think that Cambridge Analytics are the only ones who did this and who have this data. Shutting down CA won't stop the exported FB data from being put to all sorts of uses.