The skills forming part of the open water PADI course all have a purpose. Learning to dive is multifaceted. Some aspects are preventative, some are responsive and most are directly to do with actually getting underwater in a safe and fun way.
Weight related skills Being able to drop your weights is something most of us are unlikely ever going to need to do. But imagine being a situation that requires this. If you are able to drop your weights and know what to do then it removes an element of stress and you can remain in control of the situation. A weight belt slippage is a more likely situation to face. Again, it’s about having the confidence to respond to this situation in as calm a way as possible.
Scuba kit removal. I’ve never been in a situation where I’ve had to do this underwater (other than instructing!) but doing this on the surface is quite a common occurrence in some diving situations when you’re entering the water.
Mask skills are another “obvious” one. These are skills I spend a lot of time on. It’s one of the areas that students struggle with and it means it’s even more important to get it right in the confined water first, then the open water. If students struggle with this, and there’s an element of panic then imagine the consequences in open water without their instructor right by their side!
Gently rise and fall in a controlled manner The old fin pivot! This is early in the training because it’s all about buoyancy! If you can control your buoyancy at an early stage then the rest of the course can reinforce this learning, leading to better buoyancy at the end of the course.