Comfort and Convenience
An engine start button only replaces the ignition twist; it still depends on the key fob being recognised inside the cabin and usually on the brake pedal being pressed, so it saves a motion rather than changing anything else.
Safety and Driver Assistance
A collision avoidance system assists: it monitors the road ahead and can warn or intervene with braking, but it does not steer the car or remove the driver's responsibility to watch traffic and react.
Multimedia and Connectivity
An AUX input carries only analogue audio. It passes the sound from a headphone socket straight to the amplifier, so track selection and volume stay on the connected device rather than the head unit.