Family sharing is just replicating a feature of the disc age that valve killed of only owning 1 copy of a game and installing it one multiple people's computers. If it had DRM requiring the disc to be inserted to play (which many games did), only one person could play it at a time.

I had a couple of classmates who'd take turns buying each Sims 2 expansion because you only needed the last installed expansion disc inserted to play so that way they'd each have a fully expanded Sims 2 install at half the price. My dad would always have the latest expansion installed and I would have to wait until they got the next one before I could get that one. Certain expansions were exciting enough that I'd find times to play on my dad's computer to play the latest expansion though