[WalterBright]

A lot of accidents happen on the runway or shortly after. Video will tell a lot of things that telemetry won't - visibility, runway incursions, just where the airplane lifted off, ice on the wings, fire or smoke, any missing parts (!), open doors, working lights, bird strikes, etc. It can also be a backup if the telemetry is lost, such as speed, position of the flaps, problems with the landing gear, etc.