The stated use case for the perf improvement was "yes(1) may be used to generate repeating patterns of text for test inputs etc., so adjust to be more efficient."

Source: https://github.com/coreutils/coreutils/commit/35217221c211f3...

I've personally used it for generating repeating text and filling disks in system testing, so I appreciate it being faster at those tasks. I also sometimes use it as a signal generator for a hacky load generator, like so:

  yes | xargs -L 1 -P NUM_PROCESSES -I {} curl SOME_TARGET_URL > /dev/null

This doesn't benefit from being faster per se, but I appreciate it using less CPU since I want to give curl as much system resources as possible.