Tinted, specifically selective YELLOW ones, came from racing. Kung hindi ako nagkakamali ang dahilan ay para hindi masilaw ibang driber. May iba ring purpose.
Other tints may be useless or have no good effect.
In my case naman, hazy (yellowish) and marami na watermark yung headlights that's why nung pina-detail ko I decided to also put a film (tint) for protection na din. Med-black lang naman and not the dark one, and based on my observations hindi naman significantly affected yung brightness ng light.