You can do fc00::/7 in addition to public addresses so your lights don't have public address while your phone does.

I mean, so many reasons. Not the least of which is carrier grade NAT is out. And that alone implies so much cost savings, performance increase, and home user flexibility .

I'm struggling to assume good faith on your question, since it's so strange. I feel like I need to start from scratch explaining the internet, since asking this question reveals a lack of knowledge about everything networking.