Say you want to contribute to a project and find out the only way to do so is by discussing the issue on IRC or the mailing list, then submitting the patch per email.
IRC is fine, so are mailing lists; I use both, plus various git forges, to contribute to open source projects.
IRC is still going strong on OFTC and Libera.chat
I get that the younger folks like discord, but seriously it’s a proprietary mess that locks everything behind a wall and tries to extract payment from each and every user.
If you host thelounge using IRC is quite cool. As you get a better experience with backed up messages and stuff.