Previously, if you shared your library and someone else was playing any game, they would get ejected from said game and be unable to play any other game, as soon as you started to play any game whatsoever.

This made it more or less useless.

Now they changed it to where you can only play the same game as many times as your family collectively owns it. So, if your family member plays a game you only have a single copy of, they can keep doing so, until you start that exact game. You may still need to activate the client beta for this, but it'll be active for everyone eventually. (Don't know if it is yet, as I'm using the beta)