To create a Custom Pass Volume that affects every camera in the scene, set the Custom Pass Volume component’s Mode to Global. To create a Custom Pass Volume that only affects cameras within the boundaries of the Volume, set the Custom Pass Volume component’s Mode to Local.
You can use the Priority field to determine the execution order of multiple Custom Pass Volumes in your scene. If two Custom Pass Volumes have the same priority, Unity executes them in one of the following ways:
When both Custom Pass Volumes are Global, the execution order is undefined.
When both Custom Pass Volumes are Local, Unity executes the Volume with the smallest collider first (ignoring the fade radius). If both Volumes have the same collider size, the order is undefined.
When one Custom Pass Volume is Local and the other is Global, Unity executes the Local Volume first, then the Global Volume.