When a unit is acting, they move to another neighborhood to keep a minimum level of fire protection. They protect that neighborhood, although sometimes depending on where that units is relocated to, they may go back to their original neighborhood acting as the other company. Example, Engine 16 is relocated to act as Engine 1. A Box comes in for 34th Street and 5th Avenue. Engine 16 responds first due, as opposed to second or third due if they were in their own quarters. I hope that helps.