For most resort skiers, an extreme cold balaclava is more than you need. These are built for temperatures below -15°C (5°F) with thick fleece and windproof membranes, designed for harsh backcountry conditions, high-altitude expeditions, or brutally cold regions like interior Canada or the Alps in January. If you're skiing typical winter conditions at a resort, a "Cold" class balaclava will keep you comfortable without the extra bulk.
The downside of going extreme is overheating. Once you're skiing hard or the sun comes out, that heavyweight insulation traps heat fast, and you'll end up pulling the balaclava down anyway. The added bulk can also feel restrictive under your helmet and goggles.
That said, if you regularly ski in genuinely frigid conditions—long, exposed chairlift rides in subzero wind chill, backcountry tours where you're not generating much heat on the ascent, or ski patrol duty—an extreme cold balaclava is the right call. For everyone else, a midweight option with the flexibility to layer a lighter piece underneath on the coldest days is usually the smarter choice.