How to Properly Distribute Files in Blazor’s RenderMode.Auto?

I’m working with a Blazor project and using RenderMode.Auto for my components. I understand that this mode initially renders components on the server side and then switches to client-side rendering once the WebAssembly files are downloaded. However, I’m unclear about the seperation of main and Client pages/components,Even in the template project of visual studio (RenderModeAuto with Interactivity set at Per Page/Component), Client project has the Counter.razor page while Weather.razor is in the main project. I can't understand why there's a seperation of components between the two projects while we can simply change render mode for each page/component