I was loking for this option yesterday. I found myself in a channel i don't normally use, but lurking was prohibited. you were serverd in order of join but I had to leave and I would have never remembered the next day the channel name. Convenience would have let me /part -k #channelname then i could have easily done /join #[tab] to re-join it next morning.

Also I already keep channels open in options, but not rejoin on connect, for logon reasons.