Does anyone have any firsthand information of a weight ditching incident in which that was the only viable option?
Actually, I witnessed a situation that would have likely turned out quite different had ditchable weights not been on board. This is circa 2001.
A local guy spearfishing in the Gulf of Mexico shot a fish that was a little too big for him. Instead of letting go of the fish (cutting the line or dropping the speargun), he fought with the fish and became partially entangled. As he started to swim himself to the surface, he got a cramp in his right leg. Working harder with the remaining leg, his second cramp started. While I don't completely understand the reasons, he could not inflate his BC (couldn't reach or couldn't find his inflator), but could reach one of his weight pockets. He found himself sinking, tangled in a lineshaft line, with a large live fish attached, with two cramped legs. Luckily, he was able to ditch one of his weight pockets. He became positive enough to rise to the surface. Today, he is fine and continues in insist that he "had it all in control".
This could have worked out much worse.
Now, you can make an argument that he made a LOT of mistakes. Many of these were the result of his hard-headed rejection of principles he had learned, and learned well, 100's of dives earlier in his open water and advanced open water training. Our instructors didn't teach him, but I am sure he learned the right skills. That doesn't matter. The concept of ditchable weights is a positive buoyancy remedy for when EVERYTHING else doesn't work....including a logical thought process and adequate prevention thoughts to avoid problems.
I am personally dismayed at the current trend to "get rid of the weight" on the belt or integrated weight system for open water diving. I think it may result in a trend of additional risk to typical recreational divers. In my opinion, open water diving should ALWAYS be done with some ditchable weight. I cannot fathom a recreational, open water instructor teaching anything to the contrary. There certainly will not be one working for me.
Phil Ellis