Helicopters are relatively small aircraft with good maneuverability that can get close to buildings, and don’t need a runway to take off or land.
Police use helicopters for pursuits, Patrols, investigation, and also for supposed “crime suppression” - the notion that a visible police presence by itself will reduce crime.
Information gathered with helicopters includes photos, live video streams, 3D mapping and analysis of terrain, and visual and verbal data gathering and transmission via radio.