For most resort riders, fully sealed storm-proof boots are probably more than you need. But if you ride in consistently wet climates like the Pacific Northwest, spend long days guiding, or regularly tackle deep powder and backcountry terrain, they're absolutely worth considering. These boots combine sealed seams, gusseted tongues (an extra flap of material behind the laces that blocks snow and water), and an internal waterproof membrane to keep your feet dry in the nastiest conditions.
The trade-off is that all that weather protection can make boots run warmer and less breathable, which isn't ideal if you tend to run hot or ride milder days. They also come at a premium price. If you're mostly cruising groomers on fair-weather days, water-resistant or waterproof membrane boots will serve you just fine for less money.
Think of fully sealed boots as insurance for extreme conditions—worth the investment if wet feet ruin your day, but unnecessary if you pick and choose your storm days.