Setting up and balancing the game economy, player progression rate, and the monetization model can be a daunting and time-consuming job. In well-staffed teams, these duties are addressed by a dedicated specialist, often known as an economy designer. In smaller, less specialized teams, the heavy burden of creating a successful game economy will often fall onto the generalist game designer.
In theory, the business model of Free to Play games is simple. Lower the barrier to entry (free download) to attract a large audience, retain your players with fun gameplay, and provide them with ample opportunities to express themselves, save time, and enhance their gameplay by paying.
In practice, it's a huge challenge, especially since you're operating within a saturated market and with an increasingly savvy audience that often expects to get most of their content for free, even after playing your game for months or even years. To have any hopes of succeeding in this...