A driver should only flash his headlights to other road users to:

Flashing headlights serves a crucial purpose in road safety and communication among drivers. It is generally used as a way to warn other road users of your presence, especially in situations where visibility might be poor or when approaching intersections. By flashing your headlights, you are drawing attention to yourself, which can alert other drivers or pedestrians that they need to be cautious or aware of your position on the road.

Using headlights to signify your presence helps prevent accidents, as it can notify others that you are coming, particularly when they may not have seen you otherwise. This practice enhances overall safety for all users of the road, making it a responsible action for drivers. Other options, such as annoying slow drivers or simply attracting attention, do not contribute to safety and could potentially cause confusion or frustration among drivers. Additionally, signaling a turn is typically done using turn signals rather than headlight flashes, making it an inappropriate use of this action.