But once the engine gets started and the heating process inside the engine due to the continuous combustion is enough to sustain the vapourisation further. Hence the choke should be used minimally.
In rare occasions when the fuel is almost exhausted and there is no stock, sometimes the use of choke helps to vapourise the fuel to start the engine and go a little distance with remaining few drops of fuel residue left. It may help to reach the nearest petrol pump. But this is not good for the engine.
Using choke is not recommended for new vehicles where as it becomes must in case of old vehicles. Generally the engines are so tuned so that they use least or minimum or optimum amount of fuel to increase its efficiency and mileage.
In cold weather the spark generated by the spark plug is insufficient to cause the necessary combustion of charge(air+ fuel) causing the engine to start. So at that time choke can be used to increase the ratio of fuel in charge mixture.
This makes the engine to start with an ease. Frequent use of choke is harmful for engine as it may vapourise the lubricant oil
rupturing the engine liner of cylinder. Function of choke is just to increase the amount of fuel in air fuel mixture.
As our engines are idealized so it always try to save fuel. In case we run out of fuel choke can help to reach the nearest fuel pump with the left quantity of fuel.