When Call of Duty: Black Ops 3 makes its release in November, it will launch with the entire campaign unlocked. According to GamesRadar, every level will be available for you to jump into, without having to beat the levels before hand.
This means that Black Ops 3 won't punish your friends for a waiting a while before picking up the game. If you're looking to explore the game's co-op experience with a friend, they can jump right in – no matter what part of the game you have made it to.
You know, if you're the 'friend' that refuses to start the campaign over again with a friend and resume your single-player experience once you two are done playing together.
If you do decide to share your progressed experience with a friend, there will be perks (for your friend, not you). Players will be able to share weapons in co-op gameplay, if you have an awesome gun unlocked that your friend hasn't unlocked, you have the option of sharing your weapon with your friend. Remember, sharing is caring.