no arguments, and I've been to some great parties like that, but I've also had parties with a set guest list - mostly dinner parties, with table settings, portions, etc.
Early on, when a friend was visiting from out of town and I hosted a dinner at my house, lots of our mutual friends said they couldn't make it at the time, but would come later. I didn't have the experience to say "That's great, you're welcome to show up later for drinks and hanging out, but dinner will be served at 7:00", and I spent all night running around re-doing dinners.