Reducing weight isn't something I've ever fretted about. As long as I don't have a bunch of extra air in my wing during the safety stop, I'm good. I'm not interested in trying to get it shrink-wrapped around the tank.
Yes, I'm with you on that. Years ago I did obsess with my lead being accurate to the nearest 1lb - until I learnt to properly breathe and use my lungs correctly. Where I dive some weight in hand is considered beneficial
But this thread is about newer divers. The default is that it's always the instructor overweighting students. Why clearly there is some validity because it does happen, but that's often not the whole answer.
Unfortunately lots of Instructors don't fully understand the real reasons, and thus can never communicate it to divers.
Everyone is taught to weight check with an empty tank. It's perfectly possible to do it with a full tank before you start the dive. In this case your head should be a hands width below the surface, which gets you in the ball park. Good enough to get you dialled in before the dive.
So many people absolutely refuse to do one, because they know better - and yet you know they've got too much weight.
A new diver is generally never relaxed at the surface, they're finning and sculling, and a bit stressed and anxious. This triggers the fight or flight reflex, which subconsciously drops the diaphragm to give you greater lung volume (so you can run away from the sabre tooth tiger)
Already the diver is more buoyant, then they take a gulp full or air or are breathing in the top half of their lungs, and more than likely have problems venting their BCD (often they let go of the button too early or not in correct orientation) and have issues descending.
The "answer" to all this generally seems to be to
add more weight.
Then when they get to depth, maybe they see a pretty fish, their attention is distracted, their brain goes into normal breathing and they're suddenly negative (no longer breathing in the top half of their lungs) This causes them to add air, get stressed thus causing diaphragm to drop again, increasing lung volume, and up they go. It becomes cyclic
Answer of course = Add more weight
Maybe they'll get more experience and be self aware enough to realise they no longer need that weight and reduce it. Often not. Lots of divers even those with over 100 dives, cling onto weigh like a safety blanket
I'd seen some skinny little things absolutely determined they need X weight when they're clearly significantly over weighted, but trying to convince them otherwise can be a challenge.
When I teach PPB I make bold statements to the student that I'll guarantee they'll be removing significant weight (mostly) There's always a look of horror and disbelief - so I make a bet - A case of beer etc. I've never lost that bet (I don't' actually collect but would honour the bet if I were wrong)
The student just needs belief in themselves, and we do a lot of shallow water work where not only do they get confidence, but prove to themselves that they don't need the weight
If I had another day during OW I could build it into that course - but that's a whole different argument.
