In the snow
In Canada here I like to compete with other ppl in empty parking lots when its snowy... which is most of the time in winter. I usually turn off the o/d simply so that when I take my foot off the gas, the transmission won't shift into fourth... whenever you take your foot off the gas, the tranny shifts up. I turn it off so it wont go into fourth, and then back to second again when i step on the gas. And of course in city driving i turn it off, good for the trees. That's just my 3 cents.