I have an Ecobee rather than a Nest, but I had the Nest before I moved and the one thing I note is that it having access to temperatures and weather outside the

I have an Ecobee rather than a Nest, but I had the Nest before I moved and the one thing I note is that it having access to temperatures and weather outside the house means it can choose just to run fans to circulate the air from outside to regulate the temperature inside instead of running the heating or AC. If it knows the outside temperature is the temperature you want inside, it can just shut everything off. A dumb thermostat only knows what the inside temperature is... or more specifically, when the little coil bends to connect the electrodes, it trips the heating on until the coil bends the other way and disconnects them. If the external temperature was sufficient, your thermostat could've chosen to circulate external air into the house instead of running the heating. Also, it knows when you're not home, so it can then just shut down everything until temperatures would cause other problems such as frozen pipes. Additionally, you just dial it to where you're comfortable and if you get too hot or cold, adjust it again. It learns what temperature you like it at at certain times of day, it takes a week or two to really get to know you, but once it does, it just keeps the temperature comfortable and you rarely have to touch it or even look at it after that without you needing to go through a complex programming process like you do with most other thermostats. That's pretty much what a smart thermostat gets you. Whether or not you consider that useful or a good use case for your needs is really down to your own evaluation. I like that my thermostat is smart enough to be able to regulate the temperature in my house without needing to kick on the AC or heating, which reduces my power consumption somewhat and is somewhat better for the environment, but is also better for my wallet.