Except that mIRC doesn't know how many channels are found until the end of list response is returned. It opens the window upon issuing a LIST and waits for the channel responses. That's not annoying at all. You're evaluating this feature in the wrong context. If you look at it as: "mIRC pops up a window that it doesn't use", yes-- that's annoying. But that's not how the feature works. The window is used as a placeholder for channel information in real-time as they come in from the server. If zero channels come in, that sucks-- but mIRC doesn't know that no channels came in until it's over-- ie. after it opened the window to watch for those channels.
As far as uses for a channel list when disconnected go-- by your logic, there's no use for a channel window when you're no longer online. mIRC should force those to close too. .. but seriously, I provided two scenarios where you would disconnect and still want the /LIST results in my last post. You don't need to think at all, they're right there. Channels live beyond your IRC connection, disconnecting from a server doesn't mean you will never use IRC again. Channel information from a /LIST will still be useful. That is why mIRC can save /LIST output to text files. Go figure.
It actually sounds to me like you don't use /LIST, or haven't in a really long time. I don't think it's fair for you to comment on the supposed annoyance of a feature that you don't even use.