Cuff reinforcement adds a strip of extra-durable fabric around the bottom hems of your snow pants, right where they meet your boots and skis or snowboard. This is the spot that takes the most abuse on the mountain — your sharp edges constantly scrape against it when you walk, carve, or load the chairlift, and your boots rub against it all day.
If you ride regularly, cuff reinforcement is absolutely worth having. Without it, you'll start seeing frayed, cut-up hems within a season or two, especially along the inner ankle where ski and board edges make the most contact. Reinforced cuffs can add years to the life of your pants.
It's the most common type of reinforcement you'll find, and most mid-range and higher pants include it. If you're looking at budget pants without it, just know you're trading long-term durability for a lower price tag. For casual riders who only get out a few days a season, it's less critical, but for anyone riding regularly, it's a smart feature to check for.