I guess it depends on what you're watching. I've seen plenty of Youtube videos where the CC is maybe 80-90% right if not off completely. I don't think there needs to be a signer in the video but I imagine having a loved one in the room to translate would be helpful.

Also, I've never been to a church that has the pastor's transcript printed word for word so having a signer translating for the deaf and hard of hearing is always nice.