Before I got the 2014 Honda Accord EX-L, I though the ECON button that it has would be useful in getting better fuel economy. The specifics of its action are vague. It is supposed to optimize the air conditioning system and the throttle response, among possibly other things, to provide better fuel economy.
With the ECON on, the throttle response is annoyingly sluggish, the cruise control is slow in maintaining speed on inclines and the air conditioning doesn't chill the air as quick as it would otherwise. Overall, this is a very annoying experience. Why spend over $20K on a car with all the cool features you want and the 180+ hp engine only to be annoyed at a lack of perceived power when you try to accelerate? Why sweat in a car that does have A/C?
After driving with the ECON on for over 3 thousand miles, I turned it off. In addition to an instant relief in regards to the throttle response, the fuel economy actually didn't get any worse. I still got 40.1 MPG over 54 miles driving to work today, at up to 72 mph speeds.
The ECON mode and button in the 9th generation Honda Accord is worse than useless.