CGCookie - Normal Map Modeling for Games

https://cgcookie.com/courses/normal-map-modeling-for-games

The answer is both! The big difference between modeling with the goal of a blender animation render or 3d printing with blender or modeling for games, is the amount of geometry that you can use. Games need to run in real time at 60 frames per second at minimum, so we need game models to be as efficient as possible so that we can instance many of them in one scene, use physics, and do all of the other cool things that modern games do. But we also want our games to look gorgeous! ...and that usually entails adding a lot of detail. So the central problem that every game artist needs to solve is finding the right balance between quality and performance, so again, knowing how to create 3d models with efficiency is key. The trick that all modern games use to get more detail out of less geometry is normal mapping.