I think richer control of lighting, including color and brightness, is useful, even if 99% of the time you interact with it via the wall switch. I had Philips Hue lights at my last house and enjoyed the level of control the app gave me. I used the simple scheduling capability it had and would have used more power if they offered it. (I did wish I had more control at the wall; I only had on/off switches and would have liked to have a dimmer and a button to toggle different programs.)

I can't say I found the ability to control my lights and thermostat from beyond the local network to be compelling. I changed the Nest thermostat for my mother once while she was staying there since she couldn't figure out how to do it, and I think that was the only time I found it useful. I never set up remote access for the lights and never missed it.

Remote security will be a useful application, though. Being able to buzz people in for repairs and deliveries and other services, and know that they know they can't steal anything without being seen, is an attractive possibility.

Fine-grained control of sound is another feature I would use. I often wish I could play audio in the whole house, just one room, or certain rooms, depending on the circumstances.

Also, something I find myself wishing for (less often since Covid, but still occasionally): cameras inside my refrigerator and pantry, so if I have a dinner idea while I'm out, I know what I need to pick up on the way home.