Emacs has a function for transforming a window of text under ROT13, rot13-other-window. The Emacs manual [1] says, "For example, a review of a film might use rot13 to hide important plot points." This example was added in 2012. The source code [2], on the other hand, gives a different use case: "ROT13 encryption is sometimes used on USENET as a read-at-your-own-risk wrapper for material some might consider offensive, such as ethnic humor." This comment was added no later than 1992.

[1] https://www.gnu.org/software/emacs/manual/html_node/emacs/Rm...

[2] https://github.com/emacs-mirror/emacs/blob/master/lisp/rot13...