It's not easy to define exactly what makes a good model. Like any form of design, simplicity is the key. The more the elements, the more complex it gets. Ideally, a model should be technology independent, but there are certain ways in which eZ publish operates that can influence how we structure the content model.

Do we always need a content model? No, it depends on the scale of the project. Smaller projects don't really need a formal model. It's only when there are specific relationships between content classes that we need to go to the effort of creating a model. For example, a basic website that has a number of sections, e.g., About Us, Services, Articles, Contact, etc., doesn't need a model. There's no need for an underlying structure. It's just content added to sections. The in-built content classes in eZ publish will be enough to cater for that type of site. It's when the content itself has specific relationships e.g., a book belongs to a category or a product...