I believe the cells have a distinct lifespan and during different periods they perform different functions. So there is a time when they are specifically adept at this particular task.
The right type of T-Helper cell response is critical as well so specificity in DC signaling is critical or prooer NK activation will not be as complete as it should be. Mature dendritic cells are mobile and move towards the lymph zone if not impeded. Immature DCs are less mobile but get carried by blood stream throughout the body where they can be activated towards maturity by exposure to inflamatory signaling and antigen uptake during phagocytosis (cell destruction) caused either by certain DCs themselves or by other process. There is much more but information overload is not always helpful. Best wishes.