A use case for the 'r' suffix to the substitution command in GNU Ed?

I am running GNU Ed on Fedora Linux. The GNU Ed manual cryptically refers to an 'r' suffix for the s command, to be distinguished from the 'r' command. All it says about it is the following: >The suffix 'r' causes the re of the last search to be used instead of the re of the last substitution (if the search happened after the substitution). I cannot see its usefulness especially if one uses Ed with rlwrap, with which one can easily modify the last substitution. Can someone provide a use case for 'r' as a suffix?