In the equipment section of the D&D basic rules, it lists "light" as a weapon property of the hand crossbow.
The "light" property offers the following attributes:
Light. A light weapon is small and easy to handle, making it ideal for use when fighting with two weapons. See the rules for two-weapon fighting in chapter 9.
So, this would mean I can use my hand crossbow in two weapon fighting… Great! However, in the TWF rules in chapter 9 it says the following:
When you take the Attack action and attack with a light melee weapon
that you’re holding in one hand, you can use a bonus action to attack
with a different light melee weapon that you’re holding in the other
hand.
Two weapon fighting only applies to melee weapons! Why does the hand crossbow have the light property? What purpose is it serving?
Now with the addition of the Feats in the players handbook my question still remains. The feat for crossbow expert says the following:
Crossbow Expert
Thanks to extensive practice with the crossbow, you gain the following benefits:
- You ignore the loading quality of crossbows with which you are proficient.
- Being within 5 feet of a hostile creature doesn't impose disadvantage on your ranged attacked rolls.
- When you use the Attack action and you attack with a one-handed weapon, you can use a bonus action to attack with a loaded hand crossbow you are holding.
As you can see the feat replaces the Two weapon fighting rules, and so the light keyword is still not needed.
Best Answer
I want to challenge your approach to this. As you note, the Light property is defined like this:
This property isn't just there as a computer function — it's also part of the basic description. A hand crossbow is small and easy to handle. And it is, as far as crossbows go, ideal for fighting with two weapons. You may need special practice and training (as represented by the feat) to take advantage of it, but it's undeniably better than any other crossbow for that case.
Is it true that mechanically there are no current rules which make particular use of this property? Meh. Probably so. But it does not mean the property shouldn't be there, because that kind of mechanical interaction isn't the only reason weapons have descriptions.
It might have been more elegant from a "the puzzle pieces must fit together!" perspective if Crossbow Expert said "a crossbow with the light property" instead of "hand crossbow", but I don't think that really would add much of actual value.
Of course, there's always the possibility of future features which apply to "light ranged weapons" or the like.