I placed it there as a cleanup method; if the SpawnWeapon method is passed an ItemData that is either not equippable, or not a weapon, calls destroy active weapon to set the ActiveWeaponID to a default value representing an empty item (0), and it sets WeaponActive? to false. Finally, if there is an actor loaded into the Weapon, it destroys that actor.
The empty item id can be whatever you want, I just use 0 as a habit to reflect an empty item.