Even when you document very frugal, have limited time or resources for documentation available… you should follow one of the most essential rules of architecture documentation:

Always describe level-1 of the building block view

Level-1:

• makes the top-level structure of building blocks explicit!

• very often remains quite stable over time - as the top-level system decomposition often has little or no volatility.

• therefore causes only little maintenance or change effort…

• needs to be consistent (with respect to external interfaces) to the system scope and context (see tip 5-4 (consistency of level-1 to external interfaces))