The YouTube live chat interface and API have a lot to be desired but one thing that YouTube beats Twitch at is keeping all the chat available for any new comers to read even if they join after the live stream has been going on for hours. For high volume chat I can see that being a problem, for my streams it’s a perfect way for me to answer questions once during the stream and refer people to earlier chat to get in the habit of seeing what is going on. I really like that. The same is sort of true for IRC, but the setup to get on it is prohibitive for most beginners first finding my stream.