The purpose isn't a single, positive function, rather it's a necessary evil. These systems need power to:
* Maintain memory: This includes things like radio presets, clock settings, seat memory positions, and the various computer modules' configurations. Losing this memory every time you turned the car off would be incredibly inconvenient.
* Security systems: Alarm systems, immobilizers, and other anti-theft devices require constant power to function and protect the vehicle.
* Remote unlocking/locking: Key fobs and other remote access systems need a small amount of power to listen for signals.
* Power to certain sensors: Some sensors might continue monitoring conditions even when the car is off (e.g., monitoring battery voltage).
A *high* ignition off draw, however, is problematic. It can lead to a drained battery over time, especially if the vehicle isn't driven regularly. Therefore, diagnosing and fixing excessive parasitic draw is a crucial part of automotive troubleshooting. The "purpose" of a *normal* ignition off draw is to maintain essential functions; a *high* ignition off draw has no positive purpose and signifies a fault.
