Cargo holds carry revenue cargo, often at higher utilisation factors than the passenger cabin above. One of the key downsides of the A380, with two passenger decks and all their baggage in the hold, has been insufficient cargo space, the proportions are wrong. Airlines started using all their space, both ways, long ago (both ways because unlike passengers cargo invariably goes one way only, you need to find a different source of cargo for the return). Although you may see some freighters, and the big package express companies, the considerable majority of air freight goes by underfloor hold.