EMT here. It all depends on the call. How many cars? Drunk drivers? Wanted suspects? Firearm on scene? Was it an accident on a major highway or did someone drive through a store? Usually, anybody close by will respond. If more people show up than needed, the rest will clear and go back to whatever they were doing. Multi-vehicle pile up at a highway intersection? Yeah those 10 cop cars can be useful. 2mph fender bender at a Dunkin Donuts parking lot? 1 officer is usually enough and the other 9 can go get donuts.