On Thelanis, when we want to have a good time, we make sure to go IP and 'all welcome.' Some party leaders may be a little anal and ask you to link your gear and stats, or say 'know it'/'no first-timers,' but we usually have most slots filled before finishing.
But what to do when someone asks to join in when we're just about to complete? Should we wait for them to enter? I mean, we just want to get it over with and then zerg it again (the quest entrance is right there, so we may as well farm it), but now everyone's holding their positions and their buffs are running out.