A windproof balaclava blocks virtually all wind from penetrating the fabric, which makes a huge difference on exposed chairlifts and during high-speed descents. If you ski at resorts with long, windy lift rides or regularly face harsh wind chill, going windproof is worth it—you'll stay dramatically more comfortable when the cold air would otherwise cut right through.
The trade-off is breathability. Windproof fabrics use membranes or tight weaves that trap heat and moisture, so during high-exertion skiing—like hiking to backcountry lines or warm spring days—you may feel clammy or notice your goggles fogging more easily.
Windproof is the best choice for alpine resort skiers who prioritize staying warm on cold, windy days. If you do a lot of skinning, tree skiing in sheltered areas, or tend to run hot, a highly wind resistant option might give you a better balance between protection and breathability.