Natural language interfaces can be a great way to interact with many different systems. Instead of hunting and pecking through page-after-page of UI just to get to the setting you want to change or to define the report you want to see, you can specify it precisely in a single sentence, e.g. 'Send me a report on sales for last Thursday compared to last Friday'.
Because the system also supports a conversational interface it can ask questions back to the user to clarify what they want in a case when there is ambiguity (e.g. 'Which product do you want to include in the report?').
Dialogue: a conversation between two persons - not a form that appears on screen!
find users who logged on last year on a thu after 5pm
Commands like this can be issued from a smartphone or computer using SMS or a chat client like Google Talk. The response can be delivered back using the same communication medium or, if too verbose, if can be sent by email or as a link to a web page (multi-model communication).
In practice, natural language interfaces can be intuitive and extremely concise.