spline patch (where you define a surface with a number of curves ) is very useful for modelling stuff like car bodies.   Some people find it easier to start with a shape and pull it into place while others prefer to build the final shape directly.   Its largly a matter of personal preferance  although some depends on exactly what you are trying to build.

Whatever works for you and gets the model built without a lot of nasty geometry is the right way. At the end of the day you cant really tell if an obj file was built via box, polygon, spline or any other method , though you may see hints .