When you're bear hunting, the need for this is obvious. But even when you're deer hunting, you want to be sure that should a follow-up shot be necessary, it's readily available. If your rifle shoots conicals as well as it does ball, you might want to reserve a conical for your follow-up shot. Conicals load much more easily than ball and you don't have to worry about a patch for the follow-up. Try a conical in your gun.
Some rifles can handle both projectiles well.
A cell phone is not a traditional muzzleloading item.