It's not always better to operate delayed flights rather than cancelling. I was taking a flight recently from CVG-RDU. The plane was supposed to operate CVG-PHL and back before my flight to RDU. Weather caused massive delays along the east coast. My flight was initially delayed for hours. Then as it got worse they cancelled the CVG-PHL and back, and my flight, and all others operated by that bird after it, moved back to on time. Thankfully my flight was a Delta Connection flight, for which Delta isn't as sensitive to completion factor. If it had been a mainline flight, I feel they would have tried harder to operate those PHL flights, inconveniencing everybody downstream just to pad the completion factor, when they limited the pain to 2 flights worth of passengers by canceling.