Kinda skipped through. Really fast. Anyway, the only reason developers put trophies/achievements in their game is because, 1; they have to and 2; it sells. Even if your game sucks, people will buy it because of the trophies. If the game is awesome, it will sell on its own, however, with trophies/achievements added, it will surely sell more.
What are effective trophies? That depends on the person itself. Some like hard trophies, others like long trophies etc.
__________________
__________________
|