Here are some calculations for energy usage and savings...

The main problem with most programmable thermostats is once they are first programmed in the home, they are never readjusted for schedule and lifestyle changes. The original intent is lost as the "smarter" thermostat is underutilized. 

After purchase of a $199.00 Honeywell RTH9580WF Wi-Fi thermostat in 2015, I installed it on my home HVAC system. This is a "cadillac" color, touch screen model. A free app allows control of heat and air conditioning from anywhere there is an internet connection, whether via cellular or wi-fi.

Why did I remove a perfectly good programmable thermostat? I replaced it with a wi-fi programmable thermostat because I wanted more control of my energy usage. My lifestyle often deviated from the schedule originally set up on the programmable thermostat. I had heat and cool functions happening in hours it was not needed. 

COOLING COST ESTIMATE: MY UNIT
 > 75,000 BTU central air conditioner
 > Local cost of power: 12 cents per kilowatt (10.7 cents base)
 > $0.42 per hour

HEATING COST ESTIMATE: MY UNIT
 > Natural gas 80% efficiency furnace uses 0.73 therms x 0.95 cents per therm = 0.69 per hour.
 > Cost of electricity for the 1/2 hp fan motor is an additional 0.08 cents per hour (based on a horsepower being equal to 746 watts in common electric motors) =
$0.77 per hour

There are mild temperatures in my region:
63 degrees - 12 month average highs
46 degrees - 12 month average lows