Occlusion

Occlusion is great for games with a lot of objects. In its basic form, anything off to the sides or behind the camera is not seen and therefore not drawn. In Unity Pro, we are able to set up occlusion culling. This will calculate what can actually be seen by the camera, not drawing anything that is blocked from view. There is a balance that has to be achieved when using these tools. The cost of calculating what can not be seen needs to be less than the cost of just drawing those objects anyway. As a rule of thumb, if you have many smaller objects that are regularly blocked from view by larger objects, occlusion culling is the right choice.