Just as you should document your requirements, you should also document the emerging architecture. It's certainly not just for the sake of having documentation: it should help each person involved in the project to be more productive by making them better understand what's required from them and from the final product. Not all diagrams you'll make will be useful for everyone, but you should create them from the perspective of their future readers.
There's a multitude of frameworks to document your vision and many of them serve specific fields, project types, or architectural scopes. If you're interested in documenting enterprise architecture, for instance, you could be interested in TOGAF. This is an acronym for The Open Group Architecture Framework. It relies on four domains, namely the following:
- Business architecture (strategy, organization, key processes, and governance)
- Data architecture (logical and physical data management)
- Application...
