Eco mode will change quite a few driving characteristics (throttle response being the most noticeable) and reduce top speed, along with altering the HVAC. It can give better range, especially for heavy footed individuals. On my i3 using eco mode certainly predicted that I would get better range. To be honest, I never tested it and my feeling is that the efficiency gain is marginal if you are an efficient driver anyway (I have regen set to max and try to use the brakes as little as possible, although I still find the regen is less intense than the i3 and even after a couple months with the EV3 I can still find myself needing to the brakes for the last bit of stopping since the EV3 seems to take longer to come to a complete halt than the i3 did). For those who want maximum mileage then certainly engage eco mode, turn off the HVAC, etc, etc. Go for it! For most people, I recommend just driving the car and not worrying about it.