The bot can handle basic functions like information, change, and cancel but on more complex servicing, it brings in a human agent. The customer always has the option to request a human agent. This lets customers self service for the simple stuff but still get a helping hand when they need it.
In surveys our customers seem to like this approach with some indicating that they like being able to use something like this on their own rather than having to wait for an agent to be available. I think, as long as you give your customers options a structured first layer can be helpful as long as you give them a way out to more hands-on support.