Mainly what it will likely be used for is similar to how cell phone tower data is used today. It gives you a list of people in an area at a given time, which you can correlate with other information like whether they are there often or out of habit, and whether they are breaking a routine.

Add ALPR camera data, and a public records graph, and using those selectors against other areas means you can narrow a list of suspects fairly quickly.

Arguably, surveillance merely polarizes crime instead of reducing it, where if good people are too worried about the consequences of defending themselves, it creates an effective %100 success rate for committing crimes and an insignificant chance of eventual charges - there is little disincentive to to criminals becoming super aggressive.

London is already the most surveiled city in the western world, and yet still notorious for violent street crime. Adding facial recognition to the current regime of cell towers, ALPR, cameras at every corner, cab cameras, and public transit cameras, is meaningless.

What is most likely is that facial recognition will be used the way it is used everywhere else in the world - for political pacification, not crime reduction.