Watch a dive site for an hour and you can rank everyone in the water without knowing a thing about their certifications.

What good buoyancy actually buys

• Air. A diver who is fighting their depth breathes through a tank at nearly twice the rate of one who is not. Everything about the dive shortens.
• The reef. Nothing damages coral like a fin from someone who did not know they were sinking. The damage is invisible to the person doing it, which is exactly why it keeps happening.
• Attention. This is the real one. Depth control that runs in the background frees you to look at things, watch your buddy, notice the current changing. Attention spent on staying level is attention not spent on anything else.

Why it is undertrained

Because it is unglamorous and slow, and because it cannot be demonstrated in a classroom. A wreck penetration course sells. Twenty minutes of hovering over sand does not, even though it is what makes the wreck course survivable.

The pattern is familiar from anywhere that skills get taught: the fundamental thing is boring to teach, boring to practise, and the only reliable predictor of whether someone is any good.