I have none of these "channel listing caches" nor have I ever heard of them, what's in them?
Sorry, I just assumed people knew what I meant by the channel cache files.
They are text files, generated by mIRC, that allow you to locally view/search a channel listing once you've got it from a particular server. They simply hold the name and topic for every channel on a certain server, as given by the /LIST command.
If you don't have any, as an example, connect to /server irc.newnet.net (relatively small and easy to get channel listing). Click the 'List channel ' button, fourth from the left on the toolbar, looks like a picture of a globe. For 'Using file', type 'NewNet.txt' and make sure the 'Match text' box is empty. Set min at 0 and max at 9999, and uncheck any other options. Then click 'Get list!'. mIRC will get the list of channels on the server for you and a beep will notify you when it has finished. If you now do the channel listing again, but click 'Apply', it will be almost instantaneous thanks to the local channel listing cache.
However, go look in your mIRC directory. Yuk! A file called NewNet.txt has been created, the cache file. Now, if you never do a channel listing/search and always know the name of the channel you're going to join, I guess you wouldn't have any of these files in your mIRC dir. But for those of us who do, it ends up getting very cluttered and it should all be saved in a subdirectory!! :-)