IMO there are three uses for a helicopter within an urban fire department.
Command and control - this is so obviously beneficial I'm surprised there is any argument other than budget. When budget is an issue (All the time!), there should be an established and frequently practised use of Police helicopter assets to carry a fire chief with proven comms of his own.
Evacuation - until all buildings have safe flat roofs this'll be a major issue since taking out an aerial and spearing into the building won't help anyone. If you do have a helipad how do you control the 200 people trying to hang on to the skids of a passing AS355? A dedicated fireservice Puma, well, maybe. A reliable arrangement with a nearby military base may work. But not in the UK where we seem to be unable to properly support troops abroad with enough helicopters.
Suppression - nice idea but can even a skycrane carry enough to make a real difference? Dunno
Historic note for London - there used to be a cunning plan in place for emergency only use of the HAC cricket pitch in the City for evacuation from high rises. Any passing helicopter could join in to help. Whatever happened to that?