Conversational UIs are good for two things really - dealing with massively selection, and providing an interface for entirely naive users.
Ultimately, I see them as much an extension of search interfaces as they are of messenger apps, insofar as given a potentially open-ended number of buttons (like restaurants in your area) it's easier to ask for them in english, despite the fact that the interface has anticipate all the issues that brings (you might not get it right, your request may be ambiguous etc)
And, sometimes it's easier to use english to make a selection - particularly if you don't know how to do something that should be relatively simple, and is consequently relatively simple to describe in english ("Hotel room, turn on the lights." "I want to order a pizza."). Unfortunately, this takes both advanced natural language parsing, and equally advanced response generation. The later is much harder, and I feel generally neglected, by most chatbots and platforms, IMHO.
This makes a lot more sense when using voice rather than text, but ultimately, hybrid voice/gui chat displays are what chatbots are going to evolve to. You will ask for something via voice and in addition to receiving audio responses, you will receive a stream of UI widgets in a chat window containing supplemental information and finer grained controls, such as sliders for the color/brightness of your hotel room light, or an options menu for your pizza order.
Amazon Alexa and Google Now are already quietly doing this, for the most part, but it's going to become a much prominent part of the interaction over time.