Why does a newer diver use more weight than a more seasoned diver?

The short answer is breathing control. A newer diver is reacting to the instinct of holding your breath when your face is underwater. Although not really holding their breath, they tend to keep their lungs inflated much more than a very relaxed diver would.  Often when they exhale, they quickly inhale so as not to leave their lungs empty.  With full lungs they use much more weight to keep them balanced. 

They also tend to exhale slow but inhale quickly. Again not wanting their lungs to be short of air. Most of the time they don't even realize they are doing it.  I have seen new divers use 28 to 30 lbs of weight in warm water with a 3 mil suit and they were not fat. By the end of the weeks trip with just a little training, the same diver was diving 16 lbs.

With experience and training they relax and breathe more normally. Less weight to keep them balanced and they tend to make a tank last longer.  I share with most newer divers that continuing their training has many benefits. Less weight = easier buoyancy control which makes a tank last longer and it is a much more enjoyable experience.  

2 classes I think are mandatory. 1 Advanced Open Water. You already know how to scuba dive. Now learn skills that increase your confidence, safety, and comfort.  2. Peak Performance Buoyancy.  Master this skill and you will gain many many benefits. 

~Freddy