Why Keep Sims Happy in The Sims 2 Pets (PS2)?

You don't have to keep Sims happy, but it's highly beneficial:

• Productivity: Happy Sims perform better at work, maintain relationships, and have higher pregnancy success.
• Avoid trouble: Unhappy Sims develop depression, neglect needs, or pick up bad habits (smoking, stealing).
• Enjoyment: Watching thriving Sims is far more satisfying than managing miserable ones.

While not required to finish the game, happiness makes the experience richer and more rewarding.