In areas where violent and property crimes are high, it will be a blessing. In places where law enforcement is used mainly for supplementing municipal revenue, it will be a curse. And where the government uses the law as a weapon against dissent, it will be a nightmare.
This is true of almost any police tool. I mean you can apply to guns, pepper spray, probable cause, etc. As a blanket statement reply: It really comes down to implementation and training.
Really though, i'm not arguing for or against face recognition in local law enforcement. As a biometrics researcher i love to see real applications that actually work for the community, but as someone who disagrees with mass collections, outside of the obvious, such as a license photo or voluntary admittance to a NEXUS/TSA pre-check/Global Entry program, i worry.