I don't know about useful, but the most visible one is copywriting. Even when there's a human involved, every startup/small org I know runs content through them. (And that includes this article.) It's definitely something that companies want even if they don't necessarily need it (like analytics).

By far the best AI+human customer support mechanism I've experienced is through SMS/messages. They support auth, they're asynchronous, there's no app or custom interface to timeout, it's easy to send complex queries as text and you have the log right there. Apple does this really well. Delta also does, surprisingly, because their AI phone bot is garbage. It's also presumably easier for the human agents to multi-task.