It costs quite a bit to maintain an empty house at a comfortable temperature. It also takes a good while (order of hours) to converge on that comfortable tempe

It costs quite a bit to maintain an empty house at a comfortable temperature. It also takes a good while (order of hours) to converge on that comfortable temperature if you haven't run the HVAC in a long time and the weather is extreme. The ubiquitous programmable thermostats do different things at night, in the morning, during the workday, and in the evening. The idea being that the temperature is allowed to drift when no one's home, but is brought back in line by the time someone is in the house again. However they are a PITA to program (tiny cryptic LCD, 4 buttons) and basically useless if you don't follow a consistent daily routine on the weekdays. Nest's value proposition is to be smarter about when the house is actually occupied/going to be occupied. Also when you're traveling (or if you have it in a rarely-used property) you can remotely start the heat/AC when you're several hours away so that it's comfortable by the time you get there. I have none of these problems, so I don't have one, but they do solve a problem that some people really have.