It's probably just in endurance races. There is a trophy to earn where you have to finish a race with under 1% fuel remaining. One of the coffee breaks involves fuel as well.
I got that trophy doing that coffee break event. You had to drive the Nurb GTR (can't remember the exact name but its a racing one) with only 1 liter of fuel. You had to reach a certain distance (3,500 meters) with only that fuel, lot's of coasting.
Weird, because I thought I was below 1% when the time ran out too. Oh well, I'll do it again!