What advantages do focused Arrows of Slaying have over more generic ones?

Question

I was looking at the arrow of slaying magic item and part of it intrigued me (bold for emphasis mine):

Some are more focused than others; for example, there are both arrows of dragon slaying and arrows of blue dragon slaying.

Is there any mechanical benefit from having a more focused arrow?

As it doesn't impact extra damage from the magic of the arrow, I don't get what the advantages would be of having more focused arrows.

The only thing I came up with, is that these arrows are not to be created by players, but more often found as loot/treasures. Given that, a more focused target will restrain the number of situations where the player can use it efficiently.

Is there any benefit I missed?

Note that I am asking about the mechanical benefits that more focused arrows might have over more generic arrows, not about designer reasons for why these kinds of arrows exist.

Answer 1

Lore and In-Universe Story Support

Not everybody who crafts a magical item is equal. If some ancient riverside civilization was tormented by a black dragon named Smog, they may very well task one of their greatest bardsmiths to make an arrow to deal with the creature. Said bardsmith may very well go "Okay, I need to make an item that works great against black dragons!" and focus on that concept, never figuring that there'd be any reason to make the arrow work equally well against green dragons.

If you as a DM hand out a quiver of Arrows of Black Dragon Slaying, or perhaps even Arrows of Smog Slaying, you're essentially telling a bit of a lore story on the items found. It makes the item less useful to the party in general, but if it later turns out that Smog is still alive and your bard is a long-lost descendant of the old bardsmith, the item suddenly has a lot more meaning.

Inter-dragon conflicts

Smog needs to be brought down, everybody knows that, even Blue the Blue Dragon. Blue wants his kobolds to have the best possible chance to bring down Smog, but he doesn't want the kobolds to pose a risk to himself. Instead of making them all Arrows of Dragon Slaying, which could be used against himself, he instead gives them Arrows of Black Dragon Slaying. Now his minions are more useful against his nemesis Smog, but they don't pose more of a risk to Blue.

Answer 2

Scope limitations

Theik provides a very nice example, but in general, the mechanical implications are in limiting the use of the arrow.

A DM may simply not want it to be more general use and plans(hopes?) you use it in a very specific situation where you'll really need it. There can be many reasons for this, but the mechanical benefit is more for the DM to dictate when it can be used rather a mechanical benefit for a creature.

However, one could say that the mechanical benefit is to help guarantee it's use when the specific need arises and not just when the creature has a general opportunity.