"Please buy tickets to concert"
"Front row tickets to concert purchased for $500"
"Wait no, buy the cheapest tickets!"
"Cancelling order! Purchased last row tickets for $10"
"Only $10? Well maybe I can spend a little more an not be in the last row"
etc
"Alexa, book me a flight to Sydney for Wednesday"
Alexa knows that I'm in Melbourne, that I always fly economy class on flights under three hours, have a strong preference for Oneworld airlines, fly direct whenever possible, and like to fly in the mornings except between 8am or 10am on weekdays.
"I found three flights on Wednesday that match your preferences. On your kitchen screen now. Which one shall I book?"
The next development after that would be intermodal transport scheduling and calendar awareness: "Alexa, book me travel for the Sydney board meeting". "Here's an itinerary that matches your diary and preferences."
However, that is besides the point. This was just an illustration of what is possible if your VPA is a preference-aware negotiation agent.
Of course you are free to choose a closed platform, but it doesn't have to be that way.
Currently, i only use it for alarms. I'd love if Assistants became good enough to conversationally text someone.