mick41 for spam prevention, setting to just 1 post and leaving discussions to auto should indeed be enough. Unless you have some very creative spammers that try working around it by making convincing innocent posts first. But I guess most spammers aren't even aware that this extension is active in the first place.
I think some forums appreciate the ability to set a higher number when the extension is used as a quality filter instead, where they want to moderate new content from users until they become more "trusted".