It protects your games from moisture
Sleeves also protect your cards from the bane of most paper products: moisture. We can’t help it if our palms are sweaty, especially if we are playing an intense game of social deduction (it’s hard to lie!). Sleeves give you peace of mind. You don't have to worry if the table is slightly damp from a drink or heavens forbid, someone accidentally spill on it. Board games are very social so we tend to eat/drink when we play. Save yourself from the heartbreak of replacing a whole deck just because someone accidentally bumps his/her drink on a card.