The Hidden Blade Assassin's Creed in Depth

When you reach Level 15 in Assassin's Creed Odyssey, you acquire a second Weapon Slot, which means you can equip two weapons at a time, and switch between them at the press of a button. While this is nice for players who seek a bit of variety in their gameplay, and like to swap between weapon types, another reason you would want to do this, is to put a weapon you will rarely ever fight with in Slot 2, and use it as a Stat-Stick.
Other than Elemental Effects, like Weapon Damage Becomes Fire Damage, or Weapon Damage Becomes Poison Damage, Traits and Statistics that are part of a weapon apply to your entire character even if you do not currently have that weapon held in your hand. All you need is to have it in one of your two weapon slots. An example of this, for those of you who have seen the previous video, is that having the Trident in a slot, even if you never select it, will still let you breathe underwater. Because you don't need to hold the weapon to access its stats and benefits. This frees you to take advantage of its properties, while still using a weapon you actually enjoy more.

When you reach Level 15, there is no reason not to have a stat-stick in Slot 2, because to leave that Slot open means that you are throwing away bonuses to your various Damage types, or sacrificing the ability to have additional, unique benefits that you would get from putting a Legendary Engraving on that second weapon. Remember, you don't have to actually use this weapon in combat, just make sure you leave it in a slot. Maybe it's a weapon-type you hate and wouldn't be caught dead playing with, but that's okay! Its abilities and stats apply to the rest of your character even if you just leave that weapon in the background.

As another example, a weapon that gives Assassin Damage, even if you never actually make attacks with it, would benefit you as a Stealth player, because the simple act of equipping it will raise your Assassin Damage, and thereby make your Assassinations and all Assassin Skills, hit much harder.