The human body is neutrally bouyant. Dive suits, wet or dry, are positively bouyant. Therefore, when wearing a suit, we need something heavy to keep us neutral. Some people have such heavy cylinders, they don't need anything else. Most of us, however, aren't this lucky, and so we have to add lead instead.
I realised very early on just how moronic the weight belts I learnt to dive with were. The way they came undone twice while I was learning was a good hint. In my stab jacket days, I made sure I wouldn't loose my belt by clipping it to my jacket, so even if the buckle did come undone, it would be a pain, but not one that resulted in me rocketing to the surface. When I moved to a wing, with a harness made entirely of weight-belt webing, my options expanded dramatically.
My current setup for weight is:
All my weight is fixed - I cannot ditch it whilst diving. I don't see the need. The only time I've had the weight ditchable was when I was using the D-weight, which weighed 16lbs. The difference between having that monster attached or not attached was significant. Keeping the V-weights ditchable would make maybe 8lbs difference - not enough to be worthwhile.
Unlike most people, my cannister torch is not part of my weight.