Or any other place where privacy is important and you want to share a crowd shot or want to take a shot where there are unfortunately people in the background. Which is pretty much the default for me in public settings / where I don't know every person in the picture personally, but in particular, hacker conferences are the kind of place that comes to mind.
I guess the photographer should (for the foreseeable future) always double check that it got each of them (perhaps by having the algorithm produce a second picture with green squares around detected faces), but that's peanuts compared to having to open up an editing program and blurring the region or even each face individually (try doing that on mobile), and blurring looks much worse.
