If you are going to dedicate some time to designing the architecture of a software system, and not just let it emerge after implementing features, you should do so in a systematic way.
Software architects need to ensure that the architecture they are designing will satisfy the architectural drivers, and a systematic approach can assist in accomplishing that goal. In Designing Software Architectures, A Practical Approach, the following is said about using an architecture design process:
"The question is, how do you actually perform design? Performing design to ensure that the drivers are satisfied requires a principled method. By "principled", we refer to a method that takes into account all of the relevant aspects that are needed to produce an adequate design. Such a method provides guidance that is necessary...