In a word: hilarity. You probably noticed this while playing, but the AI in The Sims 4 isn't exactly the brightest.
OfficialNerdCubed decided to start a game of The Sims 4 where an entire household was randomised -- and then he followed the characters in the house, reality-TV style. No interactions, no helping the sims out, no commands. He just watched. Immediately, people fell in love, the house almost burned down, and nearly everyone refused to clean or fix anything.
Really, without players, sims have a hard time being happy or healthy. They become slaves to the most random whims. But don't let that discourage you! If you can let yourself be a simple observer in the game, you'll be privy to heaps of fantastic if not downright silly situations.
Nerd³ Plays... The Sims 4 [OfficialNerdCubed]