Yes, facial recognition could help cops identify a robber more quickly and yes surveillance has been used to expedite investigations, but what we've seen is that cops across the board will disproportionately abuse this sort of technology to track and monitor (and sometimes later harass) protesters, activists, ethnic/religious minorities and the undocumented.
Here's one instance at the federal level, but abuse happens at the state and local level constantly.
https://www.theguardian.com/us-news/2017/feb/10/standing-roc...
There are ways of cutting down on racial profiling that don't require turning our city into a panopticon.
Source 1) https://hoodline.com/2019/04/crime-is-on-the-rise-in-san-fra...
Source 1b) https://www.ppic.org/publication/crime-trends-in-california/
Source 2) home burgled twice so far in 2019
Property crimes are obviously way up even if violent crimes aren’t so much.
I think this conclusion is due to missing some of the downsides. Could it cut costs and speed investigations? Certainly! But try to imagine some of the creative ways in which a naive implementation could be abused.
I think everyone who supports the ban and all the supervisors that voted for it have never been a victim of a crime. Or at least never been a victim of a crime recorded on camera.
I bet 99% of the people who have been a victim of a crime that was recorded on camera and yet nothing was done to catch the criminals would be in favor of using facial recognition technology by the police.