What happens if the balance is not precise in energy balance?

You will gain or lose weight.

A pound of fat has 3500 calories. The average person eats about 2500 calories per day or about 910,000 calories per year. This means that in other to keep weight gain or loss to within a pound per year you need to balance the energy input and output to within 0.4%. That's pretty amazing and probably explains why people tend to gain a few pounds per year.

Every 10 calories per day extra you consume results in a weight gain of 1 pound per year (that's 1/4 of an Apple).

Changing the balance by 500 cal per day will result in weight loss of 1 pound per week. That can be done with skipping one snack and and walking for 30 minutes..