The most important thing, from a performance perspective, to consider when developing a Unity3D game for iOS devices from a performance perspective is culling (not rendering objects that are not visible to the camera).
Put another way, it is not what the player sees, but rather what the player does not see that most affects the performance of our game.
There are several ways to achieve culling in Unity3D. They are given as follows:
Frustum culling is always on, and essentially, culls whatever is not inside the camera view. However, it does not cull things that are in the camera view, but hidden by other objects.