This rule has to do with preventing lung expansion injuries. The idea behind this rule is safety. If a person holds their breath while diving and they ascend the air in their lungs will expand and cause injury or death. That being said, the rule was never intended to cause fear of breath control. If you hold your breath for a moment while underwater and you are not ascending the likelihood of experiencing a lung expansion injury is minimal. It is the continued practice of holding your breath doing so while moving, and holding your breath for long periods of time that cause the most problems.
There are many underwater photographers who hold their breath the moment they take the picture in order to make sure conditions are perfect. Other people have accidentally held their breath while posing for a quick underwater photo and been ok. Again, we do not advocate holding your breath while scuba diving as it is very dangerous and has the potential to be fatal. We are simply saying that if you find yourself in a situation where you think you may have held your breath on a dive for a brief moment, chances are you are going to be ok, but you should still follow the rule and make sure you breath continuously while diving.