Architecture serves both technical and organizational purposes.
Modeling the system at a high level facilitates communication of the high-level system design or architecture. The reduction in detail makes it easier to grasp the assignment of significant system responsibilities to high-level structures. In large systems, developers cannot efficiently understand the details of the entire system. They need a detailed understanding of the more narrowly-scoped portions of the system that they work on. But without an understanding of the responsibilities and interdependencies of the higher-level structures, individual development and optimization of the substructures will tend to result in a suboptimal system.