I double-clicked on a person’s face and was shown a low-res image, because the image was on an external drive that wasn’t connected.
I then had to double-click the picture to get back to the face again.
It would be useful to have the option of showing that the face was related to an offline picture, to save double-clicking there and back. So, not something that is necessarily always there - you can flick the option on/off.
This is just an annoyance- and time-saving feature.