because you can always use equip slot "" to remove a slot item.

Prime example are for RNG/THF/COR to unequip a ra/ex ammo piece so they will not accidentially shoot/throw it.

And then there are the other example, when you wanted to equip 2 of the same rings (again i.e. 2 RACC rings, if you dont tell it which finger it is to go onto, would the system just put 1 on and ignore the other then)?

And lastly, there's no way in hell I'm going to go edit through 20 books of marcos. And I'm sure majority of people who uses macros would feel the same way.