For me, it's just peace of mind. I need to know that if cloud servers go down, or even my internet goes down, my house still works. My Nest thermostats are currently cloud-only (the only parts of my house left that are), and I had to write a script to never update them exactly on the hour. That's when their API is very likely to 500; I'm guessing because most people have automations trigger on the hour.

I guess I can sum it up like this: I only want to deal with my own problems in my free time in my own home.