Forty poounds? That is a lot of lead. Why are you carrying around what is usually about two weight belts?
The bags come in a number of different weights [10, 5, 4, 3, 2, and 1]. To keep balanced I need two sets of identical weights, one on each side of my weight harness. Depending on water temperature I wear more or thicker layers of wetsuit; my body weight and percentage of fat varies a bit over time; and as my gear load varies it can go from positive to negative buoyancy.
To achieve just slightly negative buoyancy for freediving requires a bit of weight experimentation each time. Over the years, I have needed as high as 32 pounds of weight and as little as 22, and most of the stops in between. To be able to get the right weight set, ranging so far from 16 pounds a side to 11 pounds a side has required assembling a collection of weight bags. Plus, to be prepared, I carry a few more pounds of weight than I have needed to be on the safe side - and occasionally to help a diving buddy get it right.
It sounds more complicated than it is in practice. You get suited and geared up, guess at the weight you need, load the bags into the pockets on the harness, and get wet. If you immediately bob to the surface or sink to the bottom, you adjust the weight load. I takes a few minutes but fine tuning lets you move almost effortlessly in the water column and prevents the use of energy and beath struggling to maintain position.
More than you ever wanted to know ....