After becoming certified as an Open Water Diver, I first completed the Enriched Air Nitrox (EAN) specialty. For simplicity’s sake, nitrox gas is safer to breathe at shallower depths than the air we breathe up here on the surface. I have now completed my second specialty, which was the Perfect Buoyancy course.
Buoyancy is important for several reasons. First, you consume air more efficiently, which means you can stay underwater longer. Second, you control your depth so you do not damage delicate corals on the sea floor. And, third, you move more efficiently, minimizing resistance against the water.
In every way, it is a great course to take. It is also a fun course to take, because the exercises are challenging. It is very rewarding once you can master your depth and body position.
As a dislaimer, I’m not sure anyone has “perfect” buoyancy after taking this course. However, you should definitely have greatly improved buoyancy after this course, as well as greater and greater buoyancy control over time.