memes

That is the simplest possible thermostat and works great for setting a temperature, but that's not the ideal thermostat. The temperature your house "feels like" also depends on humidity. You may also care about the temperature more in a spot further from the thermostat and getting accurate measurements in that location can save you money and waste less gas. There is also the decision of how long you should run a furnace and, in the case of multiple stages, which stage you should run, although some furnaces control the stages themselves. Then there is air flow. Controlling the fan separately is useful if the house doesn't evenly heat. Sometimes you can just have the fan turn on more often and use the actual furnace less, saving gas again.

Also sometimes it makes sense to heat your house slightly more during high demand hours to save money. I dunno there is just a lot that could be done with an intelligent thermostat, it's one of the few things that makes sense to make smart to me.