OK, I hope to clear up the confusion pple have with this OD thingy.
By default (meaning no lights/indicators showing on dashboard display) - OD is on. And this is the recommended setting. It means your car is able to go to the highest gear, hence theoretically highest speed for the same engine RPM.
If you press the OD button, something will be lighted up on the dashboard - that means OD is off. The light on the dashboard regarding OD is a warning light (like the door-open light, hand-brake light, high beam light on the dashboard). So, it is a warning that your OD is off, and you should set it back to "on" unless you are sure OD "off" is what you want (just like high beam light).
So, when should you set OD to off? My personal opinion is that you should only set OD to off when you are climbing a slope,
AND find that the gearbox is shifting up and down without settling on a particular gear. Because when the gearbox shifts up, there is not enough power to go up the slope, and the gearbox will shift down to provide more power, then find that the RPM is high enough to shift up, then tries to shift up again. So, to prevent the gearbox "hunting" for the correct gear to go up the slope, you should set OD to off to prevent it shifting to the highest gear resulting in insufficient power and then shifting down again.
Hope that clarifies things.
As you may notice, I was only talking about AT cars generally. I have no idea how relevant this OD/SPORT thingy is with CVT cars, because CVT cars generally don't suffer from this "gear hunting" problem.
You also should not think that having OD off lets you accelerate faster, because it doesn't. It just prevents the use of the highest gear. To accelerate faster, for most modern AT cars, you just depress the accelerator harder to make the gearbox shift down.
Experts, correct me if you find anything wrong about the above. I'm still learning as well.
