This question has been bugging me ever since the few minutes I spent joining several Stack Exchange sub-sites whose subjects fell within my interests and thus I expect to be active in within the foreseeable future (19 of them, to be exact): How come the Authobiographer badge is auto-unlocked across all SE sites (i.e. you only need to complete one "About Me" section), but the Informed badge has to be unlocked separately for each site despite the Tour page being virtually identical in each case? Not that I'm complaining, but is there an actual point behind this redundancy?
When you fill up the About Me section of your profile, and hit save to all communities, it pops up a green notification tab right above the save button saying:
Saved to all communities
This means that when you join a new community, you already have filled up your About me section for that new community, since you saved your profile for all communities.
That is why you earn the autobiographer badge by default.
On the other hand, guidelines for posting are really important to every Stack Exchange sub-site, so making sure you read it is a priority. That is why you have to go the extra mile by taking the tour of the new community you just joined, and you earn a badge every time you read it.