Weights help to counteract the buoyancy added by neoprene wetsuits/drysuits as well as a persons natural buoyancy. Because neoprene is a foam-like material filled with millions of bubbles, wetsuits float making diving hard to impossible without weights to offset the lift of the suit. Generally, the thicker the suit, the more weight needed.
Weight belts come in several different styles and sizes. Nylon belts either plain or with pockets are suitable for SCUBA diving or snorkelling and are a cheaper option while freedivers & spearfishers prefer rubber or silicone belts as the flexibility allows for deep breathing and the belts don't slide around as much when duck-diving. most rubber or silicone belts have a "Marseille" style buckle which can be quickly releases and fall away if needed.
