Laravel自定义枢轴使用（扩展模型或扩展枢轴）

I am really stuck using a custom model for my pivot, and don't understand why can we make a custom model for it if we can't use it as a model. I've seen many answers and articles, and all chose to extend Pivot or Model, but real life usage is never taken into account and never go any further than giving it a "named" class.I am really stuck using a custom model for my p