But I think there are a lot of people that are using SketchUp for designing buildings? So when you make a good door or window component, that you can use in every opening, it is not very useful. When you have 5 doors with different dimensions, and you want to make a change in your component, you have to make this change in all the 5 components? The advantage of components is that you can work faster and you don't have to make to much adjustments.
In every case, the DC's are still useful, but I think it could be more useful if 1 DC could have different "shapes" in the same model.