What are the principal advantages of creating a conceptual design model using masses before diving into the detailed design and building element modeling?
The principal advantage of creating conceptual design models is to create a general idea of what do you want tour design to look like. It also gives you the opportunity to easily design multiple options before going deeper into detailing. Also, web services like Forma have various analyses which can impact your design decisions. In general words, it is a relatively fast way to create a concept model and various design options.
Should all buildings be modeled first using conceptual masses?
When is it needed/appropriate? And when not?
For example, should you create a conceptual mass model of a small house?
It is probably more appropriate to model buildings as conceptual masses for larger buildings like apartment complexes, large offices, commercial centers and so on. A conceptual mass design for such structures can give you a good understanding of how it fits with the other structures, how does it impact the wind, sun hours, etc. For large buildings it is also more efficient to create various design options using conceptual masses rather than a detailed design.
For a small house on the other hand, designing it using conceptual masses is not really necessary as its scale is much smaller. Thus, for a small house, it can be designed in greater detail straight away.