The worst thing about someone joining the trio, is that the someone is normally Harry's girlfriend, Hermione's best friend, Harry's twin sister etc.

How many fics have I flamed that have this sort of thing?

I think that the Trio should STAY the Trio, without outside interference, and certainly not some gum-chewing, wandless magic doing, hair flipping, large-smiling, teaches-Hermione-new-ways-to-do-her-hair-so-that-both-of-them-are-now-the-prettiest-girls-in-Hogwarts, brainless, tries too hard to be cool, and in the end is just another author spinoff twit, thank you very much.