To the best of my knowledge,you should drive with OD on (dashboard clear) if you are interested in saving fuel especially if driving at over 80kph.
If you drive the car with overdrive off, it will force the car to stay in the lower gear(gear 1-4),wont go to 5, giving you more power, but will hurt your fuel economy slightly.
Formally employed people often live their employers' dream & forget about their own.