Directly driving a user's device (or a device hooked up to a user's account at least) means an AI can do any task that a user can do, tearing down walled gardens. No more "my car doesn't allow programmatic access so I can't heat it up in the morning without opening the app."
Suddenly telling an agent "if it is below 50 outside preheat my car so it is warm when I leave at 8am" becomes a simple to solve problem.
Complete AI control over a personal phone. Anything a user can do the AI can figure out how to do.
That is the end game for everyone right now - a new class of ambient AI powered personal computing.
The idea is a fully personal AI that can control ones devices to accomplish complex tasks. Rabbit is working on this through their rabbitOS project, lots of other players are doing the same thing. OpenAI is trying, and lots of open source projects. Even homekit has initial support for LLM integration.
IMHO controlling a phone directly is the best path forward. Google and Apple are best situated to exploit this, but they may be unable to do so due to structural issues within the companies.