A high warmth base layer is a solid choice if you regularly ski in cold conditions—think 0–15°F—or if you naturally run cold. The thicker fabric traps more air for insulation, which makes a real difference during those long, windy chairlift rides when you're sitting still and not generating much body heat.
The catch is that same warmth can work against you during active skiing. If you're charging hard or the day warms up above 15°F, you may overheat and sweat more than you'd like. That moisture can actually make you colder later when you stop moving.
The best approach is to pair a high warmth base layer with a lighter mid-layer and a jacket with good venting. This lets you dump heat on the run down but stay cozy on the ride back up. It's much easier to cool off than to compensate for a base layer that isn't warm enough.