Congratulations, you've successfully completed your PADI Open Water Diver Course and you're now qualified to dive with your buddy anywhere in the world. So the question is;
The answer of course is, you don't. If you are more than happy to dive to your current depth limit of 18 metres, then good for you. At that depth you'll get to see all the coral reefs and colourful fish you can handle (Not literally I hope!). You'll see Parrot Fish, Clown Fish (Nemo!) Sea Anemone's and miles of stunning coral without dropping deeper than 18m. But of course there's so much more to see in the World's Oceans than what's in the first 18m. Some of the bigger animals live at deeper depths and shipwrecks are more intact the deeper you dive because there's less wave action to damage them. The point of the PADI Open Water Diver Course is to provide you with the
basic skills to allow you to dive safely to the 18m depth limit but no deeper.
The PADI Advanced Open Water Diver Course (AOW) expands on those basic skills and takes them to a more advanced level, hence the name. The aim is to give you a taste of some of the different types of diving that you might want to get into whilst at the same time providing you with a qualification certifying you to dive to a maximum depth of 30m. It will allow you to confidently dive to those depths without you feeling the need for that reassuring presence of an Instructor or Divemaster to escort you. Wherever you're looking to dive in the world, you'll almost certainly require the AOW certification. The shallow wrecks have generally been deliberately flattened as they constitute a shipping hazard. We therefore, have to dive that bit deeper in order to visit the more interesting wrecks that are out there off our coast. This of course applies to the majority of wrecks both home and abroad and they attract a vast array of sea life from coral to large pelagics and other marine creatures. They are a complete world in one 60 minute dive and if you're into diving, you're gonna' get into shipwrecks. The ideal depth for most divers to visit is somewhere in the 20-30m

range as this gives great diving conditions with a reasonable bottom time on a reasonably intact wreck. Of course you don't have to dive that deep everytime you go diving, it's up to you and your buddy. But what if there's a particular wreck or reef trip that you would like to dive but the stipulation is AOW divers only? That's very common and for insurance purposes, not only will the dive operator refuse to take you if you're not suitably qualified, your insurance company are unlikely to pay out in the unlikely event of an accident. Two very good reasons alone for this certification level.