Sometimes you'll start typing a complex command line and then realize that you can't execute it now. Perhaps you're in the wrong directory or you forgot to map the drive. It would be a shame to hit ESC and lose that command line.
What I do is edit the line to insert the word "echo" in front, then hit Enter. (Note: This doesn't work if you have command line redirection.)
This prints the command to the screen, where it can be cut/pasted later. Even more, it enters the line into the command history, so a few uparrows will bring it back.