@mileagejunkie Say one has a sensor out front that automatically turns on a light, and the motion sensor can be turned on or off with a switch, I personally wouldn't rely on anything cloud based, and while I understand some might be, I think you can understand there's a place for something more reliable then that.
Now regarding your question, say you had a lamp on a plug, or really any smart switch / relay is identical to a plug, and instead of every Shabbos and Yom tov having to schedule your lights for the meal you can set it up that every Yom tov the lights stay on at night and for the meal during the day, or specifically on the first night of pesach I want it on till 2am etc..
What about light switches that are unresponsive on Shabbos and YomTov?
Definitely that can be easily implemented on a plug or light switch (considering you have the correct one..)
It would have to be thought out, on a smart plug I would make it the button doesn't do anything, while on a light you may want to override it by say clicking it 3x rapidly, since it's not like a plug which can be removed from the wall easily.