Since apt runs here on mass storage starved small single board computers, I do indeed consider `clean' one of the important apt subcommands, as in "most used", yes. I disagree with the notion that documentation incompleteness and referral to other documents is preferrable to "distraction" by information. After all, one peruses a man page for obtaining information, not for minimising distraction.
But the man page flaw is, IMHO, not the lack of complete documention of `clean' functionality. Instead it is that it's not evident from the man page that this subcommand is understood and executed. There may be other supported subcommands, about which I don't know from reading the man page alone - instead I may have to trial and error potential candidates (or look for other sources of information).
