when is ditchable weight necessary?

I was reading neve's recent post with much interest and had a followup question (didn't want to hijack a thread).

I use a SS BP/wings with 2# weights threaded into each of the tank cam straps (see photo - no the BP isn't reversed, just weird flash).

Anyway, I've found that I have good trim and neutral buoyancy without any additional weight (ocean with a skin or spring with a 5mm steamer). It seems that by having the weight centered in my body, I require about 3-4# less than previous dives with the BP/wings.

Do I really need to move some of this weight back down to a belt or can I go without a belt? My concern is that I could tear the bladder deep and become extremely negative. What is a "balanced rig" and how do you determine if you have one?

Thanks for the input!

My personal rule is that I must have a redundant way to get positively buoyant. In addition to the BC, this might be a dry suit, a lift bag or ditchable weights, depending on the tank(s) I'm diving. It doesn't really matter which of the three I use, so long as a BC failure won't leave me with no choice but to swim to the surface against negative buoyancy.
Rick

It is important whenever you expect me to rescue you. Lately I have been towing various people (DM training) and the thing that makes the most difference to the effort involved is not the size of the victim, but how buoyant I can make them.

Of course, no-one ever plans to be a victim...

Z