Excellent moisture wicking means the fabric pulls sweat away from your skin and dries remarkably fast—even after heavy output, it feels dry to the touch within minutes. This matters most if you're a hot sweater, an aggressive skier who charges hard, or a backcountry tourer climbing uphill for hours. When you stop moving (like sitting on a cold chairlift), any sweat left on your skin can chill you fast. Excellent wicking prevents that.
For casual resort skiing at a moderate pace, 'good' wicking is usually fine—you may feel slightly damp during your most intense runs, but it won't ruin your day. But if you regularly find yourself sweaty on the slopes or you're touring where drying opportunities are limited, excellent wicking is worth seeking out. It's the difference between staying comfortable all day and fighting that cold, clammy feeling.