Adjustable vents are absolutely worth it for most skiers and snowboarders. They let you open or close airflow using simple sliders or dials, so you can adapt to changing conditions throughout the day. Zip them shut on a bitter cold morning, then crack them open when the sun warms things up or you're hiking to backcountry terrain.
The biggest practical benefit is goggle fog prevention. When you heat up, moisture escapes through open vents instead of getting trapped and fogging your lenses. Closed vents keep cold air from rushing in and freezing you on chairlift rides.
If you only ski in consistently cold conditions, fixed vents may be fine. But for all-mountain riders who encounter variable temps and activity levels, adjustable vents are the most versatile and hassle-free option.