From what I understand of Vulkan, we have a render pass with its associated image resources and subpasses, and each subpass accesses those resources and may synchronise with previous subpasses to process the scene. In a 3D scene, we will have some geometry and lighting and shaders etc. we can do depth pass, deferred shading and so on - and that can all be encapsulated in a single render pass, by chaining multiple subpasses and their results together.
Excluding the scenario of tiled rendering, or when we are rendering to multiple final render targets, when would we ever need multiple render passes in a 3d scene? I understand that something like post processing or UI compositing could be implemented in a second render pass, as they need the result from the first 3d pass to present the final image. I am at a loss as to a situation whereby a game engine, let's say, would need multiple render passes, as all of its geometry and lighting and shading etc. can be drawn with the same render pass, and that render pass will contain all the final necessary buffers, like the final image.
Other than using multiple render passes as you might use subpasses (each render pass relying on the previous one in some way and each render pass having only one subpass) - what is the point?
I am very much a beginner to Vulkan and to all of these concepts so please forgive any errors in the question itself or naive notions.