Overlock or standard seams are the traditional stitched seams you'll find on most budget balaclavas. They're durable and cost-effective, so they'll hold up fine over time. The main trade-off is comfort—these seams have visible stitching with some bulk that can feel noticeable against your skin.
The real issue comes when you wear a helmet. Standard seams can create pressure points on your forehead and temples where the helmet pads press the seam into your skin. After a few hours, that irritation can become genuinely uncomfortable and distracting.
If you're doing casual resort days without a helmet, or just need something for short outings, a standard-seam balaclava can work fine. But for all-day skiing with a helmet, spending a bit more on flatlock or seamless construction is worth it for the comfort alone.