In videotape editing, operating in C-mode allows the shots on the source footage reels to be copied to the edit tape in the order they are recorded on the source tapes, rather than the order required for the finished program. So all the selected material from one source reel can be copied before loading another source reel – thus saving spooling and reel changing time. This assumes that none of the edits will need to be changed along the way!
The term lives on in the disk-based editing world where the editing disk store can randomly access the footage recorded from the source tapes. So C-mode editing on disks not only gives the advantages of faster and more convenient transfers from source tapes, but also allows the edits to be easily altered thanks to the random access of disk stores.