Beeps of pointlessness

Why do mobile phones have a setting that makes them beep every time you press a key? These key tones are incredibly annoying for everyone around, but seemingly serve no purpose whatsoever. I'm inclined to suggest that if you need the phone to beep every time you press a key when you, in fact, are the one pressing that key and (presumably) watching the screen to see the result of said key press, then you're probably not quite up to working a mobile phone yet.