An example of one benefit to having CCTV spread out over downtown is that you can relieve some police presence and spread them out to places that aren't. Another benefit would be that crimes committed in downtown would be recorded forcing criminals to wear masks rather than relying on the shock of the incident to make the victim forget details about the perpetrators features. If you have criminals walking around wearing masks then they can be quite easy to spot.
Another benefit would be in the case of this bombing. When I first heard of the bombing I was pretty interested, I wanted to know who put the bombs there, when and then who they were and what their problem was. I figured well they'll pull up CCTV and we'll all know what happened.
Instead police are being relied on to manage all of it in the moment.
It isn't a violation of freedom to be filmed in public, that's completely legal. People just start getting up in arms about it when it's a service offered by the american government for some reason. Any private individual is allowed to film for who knows what reason.