Agree with Otep. Add ko lang some details on how it works (based on observation lang po):

ECT ON:
- shift points increase depending on how hard you're pushing the gas pedal. gradual press shifts a few hundred RPM over ECT OFF, Abrupt pedal press will result to much higher shift point * ~ 4500RPM, florring the pedal results to redline shifting. Downshifting also happens earlier. Decceleration is almost always accompanied by downshifting even without pressing the brakes.

It's OK to leave 'ON' but gas mileage will be poor.