You can't play Game A when you've loaned your library to Friend so they can play Game B.
This is a way to avoid telling people your steam password to "borrow" your account, not borrow a single game.
This would have been very useful to me when, in University, my roommates and all played our games on the living room gaming PC.
I can imagine this being useful for siblings to share a game library mostly bought by parents, or a spouse playing a partner's library. So certainly not useless, but it isn't loaning a game to a friend for a week, unless you're not going to play games at the same time as the friend.
> WHEN I AUTHORIZE A DEVICE TO LEND MY LIBRARY TO OTHERS, DO I LIMIT MY OWN ABILITY TO ACCESS AND PLAY MY GAMES?
As the lender, you may always access and play your games at any time. If you decide to start playing when a friend is already playing one of your games, he/she will be given a few minutes to either purchase the game or quit playing.
But I missed the implications in the FAQ directly above that:
> CAN A FRIEND AND I SHARE A LIBRARY AND BOTH PLAY AT THE SAME TIME?
No, a shared library may only be accessed by one user at a time.
This is a way to avoid telling people your steam password to "borrow" your account, not borrow a single game.
This would have been very useful to me when, in University, my roommates and all played our games on the living room gaming PC.
I can imagine this being useful for siblings to share a game library mostly bought by parents, or a spouse playing a partner's library. So certainly not useless, but it isn't loaning a game to a friend for a week, unless you're not going to play games at the same time as the friend.