I frequently administer remote servers over SSH, and need to copy data to my clipboard. If the text I want to copy all fits on one screen, then I simply select it with my mouse and press CMD-C, which asks relies on m y terminal emulator (xterm2) to throw it to the clipboard.
This isn't practical for larger texts, like when I want to copy the whole contents of a file.
If I had been editing large-file.txt locally, I could easily copy its contents by using the pbcopy command: