an extra lap. This is from the Sierra forums:
"The reason why you want to complete an extra lap is because the race
isn't official yet until all cars get the checkered flag. If you win
a race and then stop in turn 1...the game feels it is a "wrecked" car
and would throw out the caution. Causing a yellow or being involved
with the group of cars that caused a yellow earns you an incident."