When your iPhone is in standby and you get a notification, say a text or whatsapp message and your phone lights up, it lights up at maximum brightness irregardless of what you have set in the Settings app. And once you unlock your device, it goes back to the brightness you had set in the settings app. This is useful for me at night when my phone is next to me on the nightstand and it's on silent mode. When you receive a text, you might not always feel(hear?) the vibration. Noticing the device can light up the room at max brightness, it might be a useful app for some folks like me who can't easily fall asleep at night.