Talk:Karthus/@comment-67.127.54.54-20110901035236/@comment-3358335-20110901195755

Because His ult is a channel, and if Karth is in the team fight (or near the team fight) and someone sees him when he starts it, they can interrupt him. It's ok to use if your team is fighting, and Karth isn't around, or if you are dead. But you don't want to use if you are close to the fight and alive.