Pretty simple: just automatically hides the party frame even in a 5-man party. Everytime. No options, slash commands or anything else.
Why I did this addon? Because I use party/raid addons like Grid, Decursive, so I already see the whole party (the space taken by the party frame is wasted). No I don't have/want general UI management addon (like Pitbull, X-Perl, ...).
"development" cancelled... because of a little bug (partyframe reappears when a player join in combat), and another addon do the same thing without that bug: PartyPooper