> Repeatedly typing the 'y' character into a Linux pipe is surely not that common, especially at that bit rate.

At that rate no but I definitely use it once in a while. For example if a copy quite a few files and then get repeatedly asked if I want to overwrite the destination (when it's already present). Sure, I could get my commmand back and use the proper flag to "cp" or whatever to overwrite, but it's usually much quicker to just get back the previous line, go at the beginning (C-a), then type "yes | " and be done with it.

Note that you can pass a parameter to "yes" and then it repeats what you passed instead of 'y'.