Your BCD stops holding gas at the deepest point of a dive. Your cylinder is still relatively full, your wetsuit is compressed, and your equipment is at its most negatively buoyant. Could you swim to the surface without losing control?
That is the central question behind a balanced rig. Your equipment should also let you hold a shallow stop near the end of the dive, when your cylinder is lighter. A configuration that meets one requirement but not the other is not balanced, regardless of how comfortable it feels when everything works.
Start With Correct Weighting
The first check takes place near the end of the dive. With your cylinder approaching its planned ending pressure, you should be able to maintain a shallow stop with little or no gas in your BCD. That establishes how much weight you actually need for the equipment and exposure protection you're wearing.
Too little weight can make the final stop difficult as breathing gas is consumed. Too much weight forces you to add gas to the BCD throughout the dive, concealing a problem that becomes serious if the BCD fails. A balanced rig starts with accurate weighting, not with selecting the largest wing or deciding whether your weights should be ditchable.
Cylinder buoyancy, backplate material, wetsuit thickness, and other equipment all affect the result. If you change your configuration, reassess your weighting rather than assuming the same amount of weight will still be appropriate. For the practical weighting process, see Buoyancy Control and Weighting.
Consider the Other End of the Dive
Near maximum depth, the situation changes. More breathing gas in the cylinder means more weight, while neoprene compresses and loses buoyancy as depth increases. A heavy steel cylinder, stainless backplate, and thick wetsuit can combine to make a diver substantially negative even when their shallow-water weighting is correct.
Normally, the BCD compensates for that negative buoyancy. With a significant leak or complete failure, the diver must be capable of managing the configuration without that assistance. A balanced rig does not have to remain neutrally buoyant with an empty wing at every depth, but it must not be so negative that a controlled ascent becomes unrealistic.
Your BCD also needs enough usable lift for the configuration when it is working. Lift capacity depends on the entire system, not merely the amount of lead you carry. A wing that cannot compensate for your maximum expected negative buoyancy is inadequate, irrespective of the balanced-rig discussion.
On colder or deeper dives, a thick wetsuit can actually work against a balanced rig. As the neoprene compresses, it loses both insulation and positive buoyancy, potentially leaving you too negatively buoyant to swim upward without your BCD. At some point, switching to a drysuit may be necessary rather than continuing to use progressively thicker wetsuits. A properly managed drysuit can better preserve insulation at depth and provide a separate source of buoyancy, although it requires appropriate training and isn't an automatic solution to every BCD failure.
Ditchable Weight Is a Separate Decision
I think the debate over ditchable weight often begins in the wrong place. A properly balanced rig should allow you to make a controlled ascent after a complete BCD failure without ditching weight. If releasing lead is the only way to get off the bottom under the conditions you planned to dive, I would consider that a configuration problem. That doesn't mean ditching weight is never appropriate in an emergency, but it shouldn't be the planned solution to a failed wing.
I accidentally lost weight on my second Open Water certification dive. I've never experienced a BCD failure. That personal history doesn't establish which event is more likely, but it helps explain why I prefer a configuration that does not depend on ditching weight as the normal response to a failed wing.
This isn't an argument that every diver should use fixed weight. The appropriate choice depends on exposure protection, the amount and location of weight, diving conditions, and the available emergency options. You should also understand how to release your buddy's weights if an emergency requires it. The broader tradeoffs belong in Ditchable vs. Non-Ditchable Weights.
How I Configure My Own Rig
My approach to weighting varies considerably depending on what I'm diving, but none of my configurations relies on ditching weight as the planned response to a BCD failure.
For warm-water diving with a single cylinder, I generally need little or no additional weight. When I do need some, it fits comfortably in my tank-band trim pockets. I don't have releasable weight pockets on that setup because I have no practical need for them.
My cold-water single-tank configuration uses an xDeep Zen. I previously carried weight in releasable belt pouches, but eventually replaced them with a Halcyon STA Spine Weight. I'm generally diving a drysuit when cold-water dives exceed 40 feet, giving me another means of managing buoyancy if the wing fails. With that redundancy, I don't consider ditchable weights necessary for my usual configuration.
Doubles are a different situation entirely. My doubles configuration is sufficiently negative that I need no additional weight, even when wearing a drysuit. There's simply nothing to ditch, and adding weight just to make it ditchable would be absurd. That doesn't make the configuration inherently unsafe. It does mean I need to account for its negative buoyancy and have a credible ascent plan if the wing fails.
Across all three configurations, my priorities remain the same: carry only the weight I need, distribute it appropriately for trim and body position, and ensure I can manage the equipment if my primary buoyancy compensator stops working.
Check the Complete Configuration
I evaluate a rig under three conditions. At a shallow stop near the end of the dive, I need enough weight to remain submerged without excessive BCD inflation. At the maximum planned depth, I need a credible way to ascend in control if the primary buoyancy compensator stops working. At the surface, I need adequate flotation or another workable means of staying afloat, because swimming a heavy rig upward is not the same as remaining comfortably on the surface afterward.
If a change in cylinders, exposure protection, backplate, or weight materially alters the rig, the assessment needs to be repeated. The purpose is not to make every possible failure harmless. It is to avoid building a configuration in which the loss of one buoyancy device leaves you without a controllable plan.