For me it's the simplicity and the availability of good Emacs based clients. For other services there are some Emacs clients but none of them are as good as the

For me it's the simplicity and the availability of good Emacs based clients. For other services there are some Emacs clients but none of them are as good as the IRC clients. There are also some proxy tools that let me use Emacs IRC clients to connect to other chat services, I use those when possible. This way I can do all my chatting from the comfort of my Emacs session.