The popularity of sailing in recent years can be attributed to the significant improvement in dinghy sailing clothes that make it feasible to remain warm in most conditions, even when you're soaking wet. The trick is to reduce airflow or waterflow around your body, as that would chill you out quickly.
The dinghy suit gives sufficient protection in open boat sailing to stay warm where there is a chance you go into the water, like when launching, retrieving or capsizing.
The main advantage of a one-piece sailing suit is that it stays put in the heat of the action.
When riding the trapeze you won't have a gap near your waist where the spray hits you,
or if you're dunked into the water many times.
When you capsize or take a swim, a one-piece suit doesn't float up and leave your back exposed. It stays put when you're in the water. Internal braces keep the suit sitting correctly on the body. If you overheat with onshore activities such as rigging, fold down the top or go for a swim. We use these suits often and find that they wash well.