Universal LOD System is an efficient and simple system to manage group of LOD gameobjects. The method used is designed to be as fast as possible. In consequence the time spent to manage the LOD is quasi negligible .

ULM comes in 2 versions, the free version provide the basic scripts for you to use and some examples. The PRO version provide a simple editor that can easily adapted to your specific needs.

What is happening when you run Unity.

Each LOD GameObject will look at their position relatively to the camera, and will update themselves to show the correct LOD. There is no master loop. Each LOD object acts like a robot that decides by itself what it should show to the user.