when you select the "place default folders within the project folders" option the default i/o system folders will automatically be placed in the project system folder and the default i/o media folder will automatically be set to the same folder as your project media folder.

    use this method if you want to keep the media for each project separate from the media for all other projects.

    you can always still access media from other projects, even if the projects do not share the same default i/o folders.