From a plain technological point of view, most video games fall into the category of so-called "soft real time multi-agent simulations". This means that in games, we are simulating, by stepping frame by frame, a collection of multiple interacting game entities or agents within soft real time boundaries. Or even simpler: We are moving models and actors around in our game world while trying to maintain a frame rate high enough to create the illusion of smooth movement.

In practice this imposes limits to our games' usage of computing resources, because dropping frame rates and stuttering gameplay need to be avoided at all cost. Additionally, we want our games to be able to run on a wealth of hardware configurations, even ones that do not feature top of the line hardware.

The reasons for a game to perform poorly are manifold: Inefficient algorithms, too many models and actors per scene, too much geometry to draw per model or actor, too...