Hey
I can't vote but despite that here is what I think, I am on the fence with this one because when new members come to CC they are coming looking for friends and people just to somewhere to talk, it is a bit rude saying invites only because people would just leave and not respond to a group they like, because it says invite only and it makes it harder to make friends with people that like the same stuff as you.
However, invite only is useful because an outsider entering an already establish group is great and fine but then you might not understand what is happening and the private jokes and some members may only like to discuss some things with people they feel comfortable on the forum. Plus it saves PMing friends so you have a conversation a lot easily!
I am not particulary active on any CC atm, but having CC makes it easier to talk to people without PM's and spamming on other sections of IF so either way both sides have its pro and cons so waiting for mods decision on this.