DynamiklolThey buy them to build their individual collections, mostly. Not really for specific decks, since you could just buy singles for that. You can draft the boosters with friends or just spend a couple hours just opening them. It's basically about fun, it's not often they just turn around and sell em, though I guess they could...
Why get a box instead of 36 individual packs? Packs are usually $4 each, so the box is cheaper.