A lot of us enjoy it. I wouldn't come to the DP as much without the chat nor stay on as long each day. As you pointed out, the chatting is often not serious, however, it just as often is used to discuss serious topics - including among people who don't normally use the chat. Also, if someone has a quick question, rather than making an entirely new post, they can ask in chat or form another chat room to get an answer quickly, or to discuss a topic they are interested in. As for moderation, I highly doubt anyone would ever plan a terrorist attack or something like that on the chat. I know most of the regular chatters well and they would never do such a thing.
“It is not our part to master all the tides of the world, but to do what is in us for the succour of those years wherein we are set, uprooting the evil in the fields that we know, so that those who live after may have clean earth to till." -J.R.R. Tolkien