There are two camps in open water swimming: skin swimmers (who view neoprene as cheating) and wetsuit pragmatists (who view skin swimming as theater). The honest answer is that both have a place, and the decision is mostly about water temperature, distance, and conditions.
Below 16°C, a wetsuit gives meaningful thermal protection and adds buoyancy that helps with technique. For long swims (over an hour) in cooler water, it's the safer call.
Above 20°C in calm conditions, a wetsuit is overkill — you'll overheat, your stroke gets lazy, and you'll feel chafed by the end. Skin is better.
Between 16–20°C is judgment territory. For short swims, no suit. For races or long distances, suit up. Listen to your body — cold hands and feet are warning signs.