Notably C2P was largely so ubiquitous as it was often the only way to copy or backup copy-protected commercial software you purchased. Most software came on (relatively fragile and failure-prone) floppy disks, but they were often copy-protected by way of tweaking low level parameters to the drive when the disk was written, such that data beyond the boot blocks was essentially unreadable to the standard disk read routines. The boot blocks on the disk would load the appropriate parameters before continuing to allow the software to run from what otherwise appeared to be a corrupt or unreadable disk.

C2P gave the ability to tweak those drive parameters yourself during copies, and also came with a library of known software with the necessary configuration provided. Interesting to think that it wouldn't even be legal to own or distribute anymore in the post-DMCA world.