On the Navigator in May, they also used facial recognition to identify close contacts of those that tested positive for COVID. For example, a gentleman I spoke with said he got a call to report to the medical facility because he was sitting next to someone in the theater that tested positive.
They began to use the technology a couple of days in, then it stopped around mid-cruise. I think (purely my hunch) that they used it early over the course of several ports until they had a good “database” of the bulk of passengers’ biometrics. It also did slow down the the embarkation and disembarkation processes, sometimes significantly.