While the vast majority of your dives will be completed within these depths, there are some places where you may need the training to dive between 30 and 40 meters. The objective of this course is not necessarily to go deep, but to learn how to plan your dives a lot more effectively. This will give you reduced anxiety levels knowing that you have planned for contingencies and air consumption usage for the dive.
Many of the most impressive dive locations have special dives below 30 meters such as the Poor Knights and wreck dives like the Tui and Mikhail Lermontov. The Deep Diver specialty course will provide you with the skills to be able to prepare and execute these dives safely. Coupled with the PADI Multilevel Specialty Course you can have the best of both worlds! (see the details on the ML course).
This specialty is important because you will utilise these techniques not only in deep diving activities but in most of your diving you will do.