Dr. Richard Bartle's Taxonomy provides rough guidelines for understanding the types of motivations that players have. It also allows us to appeal to those players in broad groups, for example, providing easter eggs to lure in Explorer type players. These players groups also have a natural synergy with each other: for example, killers like to prey upon achievers, so they require a population of achievers to enjoy the game. But if there are too many killers, then it gets in the way of any achievers succeeding at their own goals, so game designers have to make sure that they balance these populations by keeping track of what type of gameplay they're encouraging most when they add features.