[Kevan]

Combined positions could theoretically lessen the blow of a good round followed by a really bad one.

It will also give an advantage to a car with a bigger combined time than a car with the same combined place score but a faster combined time.
i.e. 2nd & 3rd with a faster combined time vs 3rd & 2nd with a slower combined time.  In some ways that doesn't seem fair to the car with the faster combined times.