Velcro (hook-and-loop) straps are the most popular closure on ski gloves and mittens because they just work well for most riders. You can snug them down with one hand, which is a lifesaver when you're adjusting gear in the cold, and they create a reliable seal around your wrist to block snow and cold air.
The trade-off is that Velcro isn't invincible. Over time, the hook side can collect snow, ice, or lint, which weakens the grip. After a few seasons of heavy use, the strap may not hold as tightly. Velcro also adds a little bulk compared to simpler elastic cuffs.
Still, for most resort skiing, Velcro is a solid and versatile pick. Just cinch it down properly each run and clean out any debris now and then to keep it working well.