The third reason you'll want a pocket mask as a PADI Rescue Scuba Diver is to provide in water rescue breathing for a non breathing victim. You'll find pocket mask use one of the most generally effective methods for performing this type of rescue. Under your instructor's supervision, you'll practice in water rescues with the pocket mask during your Rescue Scuba Diver course. 

Once you discover how much a pocket mask can enhance your rescue efforts, you'll want to make one a standard part of your equipment. Most types fit easily in your BCD pocket (they collapse for storage) with the retaining strap wrapped around it. Some Scuba divers like to keep theirs in a case with a short lanyard to minimize the chance of loss. Simply rinse the mask after Bali Scuba diving with the rest of your gear, and it will last for years.