The free-to-play micro-transaction business model has influenced the growth of Facebook games. This model monetizes users through small, optional in-game purchases of virtual goods. It allows games to reach a large audience with no upfront cost, generating continual revenue. Key metrics like lifetime user value, retention, and cost per user acquisition are balanced to optimize profit. Viral sharing features also helped growth, though Facebook policy changes restricted some viral channels. Overall, the model created a "digital gold rush" environment supporting massive growth for top titles and opportunities for new developers.