It is an effective tool to make you understand the relation between calorie intake per meal and gaining weight in a healthy way.
Eating random calories will not serve you to gain healthy weight. How much calories you need depend on your height, weight and BMR along with activity level.
In relation to your activity level calorie requirements also changes. If your calorie input is less than expenditure you need to work on more calorie intake.
If your calorie intake is more than expenditure then focus should be cut down more calories from your plates.