Whenever somebody makes a post on AG 2, everyone knows who posted it. This may make people avoid making posts, because they think people would think they were dumb or something if everyone knew who posted it. The administrators and Mods could see who posted it so people wouldn't troll like there was no tomorrow and could contact that user like they normally would.
That would be guest posting, this could simply be that while you need an account, no one knows who you are. Something akin to a "hide me" state I would say.
Huh? You could easily go against the rules to post with an alt. Just saying.
Allowing posting anonymity goes against the most good message boards. I don't get the point of posting if no one will see your post. Avoiding embarrassment is up to you.