Conversing with a person tends to be more intuitive than using a machine, but also more ambiguous and sometimes more difficult to get clear information. If I already have all the information I need, or if I want an opinion instead of objective fact, then going through a person can be better.

Otherwise, they're just acting as a voice interface for a GUI that I'm perfectly able to navigate on my own, and I'm not a fan of voice interfaces when dealing with technical systems.