Overdrive should be used anytime you are doing normal driving. If you are pulling a trailer, going up a steep hill, or driving in dirt, You should turn overdrive off. If you are on the freeway, in city driving, And NOT pulling a trailer, then you need to leave the overdrive ON. I hope this answers your question. Oh one more thing. If you ever get stuck in the snow or mud you will need to turn Overdrive off. Good luck