Object Folders allow you to limit a certain object type to a folder.
The advantages of Object Folders is that once you limit the folder to a single object type you can then customize the table view in the Object pane.
For example, you can customize the fields you see when you go over your Tasks list.
In the example above, you can see the Tasks Object Folder (notice the unique folder icon) with three task objects.
In the columns of the Object Table you will notice fields (E.g. "Start Date", "Due Date", "Priority") that were customized to represent a different view from the standard view available in regular folders.