Diablo – What gem bonus applies to socketed off-hand items

You can use quivers, which are Demon Hunter-specific items.

Unlike in Diablo 2, you don't need bow ammo. Now the quivers are a way to provide additional character bonuses—most quivers come with a damage boost and other magic item properties.

Class specific weapons can provide some class only enchantments that you cannot get on standard weapons. Whether or not this is worth a trade off for damage, that is entirely up to you to decide.

For instance, you can find a demon hunter only 1 handed crossbow that provides hatred regeneration or a wand for mages that provides improved arcane pool.

Like James mentioned in his answer, the demon hunter is the only class that has a unique situation where you MUST have a ranged weapon equipped or you can't use his ranged attack skills. And his one handed crossbow is the only ranged weapon you can dual wield.