Historically, you could have dirty filesystems after a reboot that "fsck" would ask an absurd number of questions about ("blah blah blah inode 1234567890 fix? (y/n)"). Unless you were in a very specific circumstance, you'd probably just answer "y" to them. It could easily ask thousands of questions though. So: "yes | fsck" was not uncommon.
It's probably still common in installation scripts, like in Dockerfiles. `apt-get install` has the `-y` option, but it would be useful for all other programs that don't.
Just to clarify: I was applying "historically" to "fsck", not to the use of "yes" in general. I can't remember the last time I've had the need to use "yes | fsck"
