Light warmth base layers are all about moisture management over insulation. They're ideal for spring skiing, warmer resort days above 30°F (-1°C), or if you're someone who runs hot and sweats heavily even in cold weather. Think of them as your sweat-wicking first layer rather than a heating layer.
The big advantage is avoiding that clammy, overheated feeling during active skiing. If you're charging hard and generating lots of body heat, a lighter base layer lets moisture escape instead of trapping it against your skin.
The trade-off is that below about 20°F, a light warmth base layer won't provide enough insulation on its own. You'll need to rely on a solid mid-layer to stay warm during cold lift rides. If you ski in typical winter conditions and don't overheat easily, moderate warmth is usually the safer bet.