@Mammmood - It most certainly does serve a useful purpose. It basically holds the bile that is left over from the digestive process of your liver as it attempts to break down fats.
Where will that bile go without the gallbladder? It may stay in your liver far longer, which could lead to bile stones, or at minimum it may send you to the bathroom more often.
Personally, I’m not at all in favor of this kind of open cholecystectomy surgery, except in an extreme cases. I think the best thing is to change your diet to include a drastic reduction in saturated fats and a complete cleansing of your digestive system.
With this surgery I think you are just treating the symptom, not the cause. Of course I am not a doctor and this is not medical advice. But I think lifestyle changes are what is really needed.