Last year my wife and I booked a direct ATL-SJD-ATL eight months in advance. Three months later Delta decided to cancel Wednesday direct return flights. VIPR changed us to SJD-TIJ, then SAN-ATL, which would have left us to figure out how to get from Tijuana to San Diego on our own (at night). There was no notification, I only discovered it by accident while checking other itineraries. I called an agent who quickly rectified the situation, but had I not noticed it would have had a nasty surprise.