The full portion of the Bash man page which is applicable only says:
If the operating system on which bash is running supports job control, bash contains facilities to use it. Typing the suspend character (typically ^Z, Control-Z) while a process is running causes that process to be stopped and returns control to bash. Typing the delayed suspend character (typically ^Y, Control-Y) causes the process to be stopped when it attempts to read input from the terminal, and control to be returned to bash. The user may then manipulate the state of this job, using the
bgcommand to continue it in the background, the
fgcommand to continue it in the foreground, or the kill command to kill it. A ^Z takes effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded.
I have never used Ctrl-Y; I only just learned about it. I have done fine with Ctrl-Z (suspend) only.
I am trying to imagine what this option is for. When would it be useful?
(Note that this feature doesn't exist on all Unix variants. It's present on Solaris and OpenBSD but not on Linux or FreeBSD. The corresponding setting is
Perhaps less subjectively: Is there anything that can be accomplished with Ctrl-Y that cannot be accomplished just as easily with Ctrl-Z?