Anon has a theory that a big part of the push for pervasive facial recognition - or at least a side benefit - is that they can easily identify potential body doubles. With hundreds of millions of faces to choose from, the chances are high they can zero in on some that could pass for twins of a high-profile person, especially with a little make-up.
You or I, just walking around meeting people in our daily life, are almost never going to encounter one of these look-a-likes. But NSA computers could find a match instantly.