Posted elsewhere, but my A/C had a small leak and was slowly loosing efficiency. At peak heat it could not keep up, but I had no way of knowing that at work. My $99 Emerson Sensi messaged me that the cooling was not keeping up and there was a problem. I could turn off the unit remotely to prevent stress on the compressor and fixed the small leak well before I would have known without a internet enabled thermostat.

I did A/C repair in college, fixing it early more than paid for the maybe 50 extra bucks wifi cost. The thermostat itself is on an isolated wifi network,