The picture demonstrates what in my opinion is the most important skill in diving: Buoyancy Control. Why? Safety for one. Start rising, air in the BC expands and you rise faster. Worst case is an uncontrolled ascent.  Staying off the reef is another reason. Avoid being stung or damaging corals. Drift diving is especially fun when you "fly" and rise above objects and fall on the other side simply by breathing. Enclosed spaces like wrecks, cenotes, caves etc can be dangerous if you don't master your buoyancy.  Your dives last longer because you don't work near as much when you are neutrally buoyant, thus conserving air. A big plus is that you don't freak out the fish you are trying to see. No flapping of arms and constant kicking to stay in place. 

Check it out here.