The purpose of eating is to provide your body with the energy it needs to allow it to perform all the processes and functions that are required throughout any given day.
If you expend a lot of energy, you will have had to have eaten enough food in order to supply your body with adequate energy levels. The purpose of eating can vary from person to person depending upon how much energy each requires for activities during each day.
If you only intend to lie in bed all day, then the purpose of eating for you will be to not have to eat that much food and you can afford to go without that much food to the extent that you'll only require a small amount of energy to maintain your Basal Metabolic Rate (BMR).
In actuality, the purpose of eating is to gain not only energy but also all of the nutrients that people require for various processes and functions that occur within the body. Essential vitamins and minerals are all accessible to you through the food that you eat so it is extremely important to eat a balanced, varied and nutritional diet.
If you do no gain these essential nutrients through your food, it is possible to get them through nutritional supplements. Although this is an alternative, it is more advisable to gain them through your food.
Some people prefer to eat a lot of food even though they only require a very small amount of energy! In this event, they consume more food than they require so they have surplus of energy. This is a sure way to increase calorie intake and gain weight. Similarly, if people eat less food than they require for their daily activities, they experience an energy deficit and tend to lose weight.
If someone eats just enough food to provide them with the energy they need but they expend energy and burn calories through exercise, then they also lose weight. This is why it is so important to combine exercise with dieting when trying to lose weight.