Question

Why is it more important to know the amount body fat as opposed to just a person's weight?

Answer 1

weight includes bones and other body tissues i.e water etc while knowing the fat also helps to know whether you have gone passed your limit. fat is the main cause of lifestyle disorders e.g heart disease and obesity therefore its best to keep it in check.

Answer 2

while checking bmi athletes and body builders maybe classified as obese since they have higher muscle mass and hence higher weight .but since no fat no increased risk for heart diseases etc.
so need for fat estimation as opposed to just weight......