When the electrical consumers are switched off, the only electrical devices that are still drawing power are the car's security system and any other devices that are designed to remain on when the car is off, such as the clock. This helps to prevent the car's battery from being drained, which could make it difficult or impossible to start the car later.
Some cars have a feature that automatically switches off the electrical consumers after a certain period of time, such as 15 minutes. This can be helpful in preventing the battery from being drained if the driver forgets to turn off the electrical consumers before leaving the car.