At The Irssi Project, fuzzing has been very effective in helping to discover bugs. Fuzzing can turn up bugs that aren't otherwise found or that are unreproducible through typical use of the program. See https://irssi.org/security/.
Of course Irssi is a client, not a server. IRC servers often have protections against frequent connections and messages, which can result in fuzzers getting kicked. So this new development in TCP server fuzzing outlined in the article is a great improvement, but there are going to be cases where the code of the server will have to be modified moreso than just swapping out the main function (which I know the author never claims to not be the case).
I thought about doing this earlier and my thought was that this could have been done with something like Scapy or at a basic level hping3.