It’s really silly that dad can’t play Skyrim in the den while junior plays Portal on his laptop.
Yeah. That is silly. The number one use I can think of for this would be to let my kid play "kid" games while I play grown up games on another computer.
Right behind that, my second biggest use would be to get 2 licenses for a game I already own and let a friend use it for a LAN party.
One of my biggest gripes about Steam is they way they handle bundles: if you buy a bundle that includes a game you already own, you cannot redeem a second copy of that game. For example, I wanted to buy the Ticket To Ride bundle, but I already own the game. So I'm basically throwing away $10 if I buy the bundle. I
If Family Sharing allowed me to own two copies of a game, I could share with my kid or friends a lot more easily. As it is, this isn't all that useful except to allow friends to "test drive" a game.