When a driver deviates from the regular track and into grass, mud, sand, or something else, they are said to be off-road. Karts/Bikes travel much slower than normal in these places, but some can trudge through off-road better than others, thanks to the Off-Road statistic. With a high stat bar of it, speed will be more abundant to get out of the situation and back into the competition. So, it can be helpful to the players who usually fail at staying on-road... it's something they'll want.