4-way stretch means the fabric stretches in all directions—up, down, and side to side—so the balaclava moves naturally with you instead of fighting against head turns or facial movements. For resort skiing, it's definitely not overkill; it's the most comfortable option, especially if you're buying a one-size-fits-all model.
The big advantage is that a 4-way stretch balaclava maintains a snug seal around your face and neck even when you're actively turning your head to check traffic or looking up the hill. Less stretchy options can gap or pull away, letting cold air in at the worst moments.
It's especially worth seeking out if you've struggled with balaclavas feeling restrictive or if your head shape doesn't fit standard sizing well. The one tradeoff is that 4-way stretch fabrics can lose some shape over time, so look for quality construction if you want it to last multiple seasons.