You'll now be able to grant 10 accounts and 10 machines access to your games and DLC, unless of course they require a third-party key or registration. The post explains that the added need to clear accounts allows a library's owner more control over who is accessing it. The change also decreases "the risk of VAC or other bans resulting from an unknown user accessing and abusing shared games on an authorized machine."
What kind of friend would troll from a friend's Steam library to the point of drawing administrative attention? Absolutely no one we've ever met, right?