surface modelling vs solid modelling
In my opinion, there is no rule when to use surface modeling or solid modeling. It depends on your style of modeling technique. Sometime surface, sometime solid. Actually the goal is how to finish your model and should the way you want. In my way, I usually like solid modeling rather than surface modeling because it generates lower error.
In my opinion , in case where you have very complex geometry like sheet structure and complex paper or concept design , you have many flexibilities to control surface to analyze the overlook and beauty of model simultaneously while designing. I prefer to go for surface modelling in most of cases and then fill it to convert into 3D model.