That is true, but I'd use my lungs to negate that effect. If I need to descend, being a little heavy I could exhale and go down (note, I said I little heavy, not overweight). Vs if perfectly neutrally buoyant, it would be a little tougher to get down during the swell up. But then again, I like being a little heavy, you can neutralize extra weight with buoyancy in the water, but you cannot negate extra buoyancy in the water without assistance.
Or maybe that's another question - neutrally buoyant at 15' (or 20') empty bladder and empty tank - with lungs full? or lungs empty?