The completed architecture for a solution is influenced by various project and environmental forces. Having navigated the minefield to get the design just right the next step for an architect is to document the architecture. Requirements, Issues, Risks and Dependencies all influence the architecture but when documenting the architecture only the architecturally significant ones are important.
A project will have a set of detailed requirements but when documenting these in a Solution Architecture Document you need to filter and roll up these requirements to a set that is architecturally significant. Each functional and non-functional requirement that has influenced a decision in the architecture should be documented but no more. The same goes for project issues, risks and dependencies document only the ones that have influenced the architecture.
Where this becomes interesting is that no functional requirements may have influenced the architecture and as such you may not need to document what the project functionally is going to do but only what non-functional requirements need to be met. You could design an architecture for a web based CRUD application (e.g. Web Server & Database) that is correct but where what data being manipulated is irrelevant i.e. the functional requirements are not architecturally significant. In this scenario you may include a level of functional requirements e.g. a use-case diagram to give context to the solution.
Focusing only on the architecturally significant aspect of a project is important so that you firstly reduce the amount of noise and secondly emphasis the factors that have influenced the final architecture. The number of possible architectures for a solution are infinite if there are no influencing forces (e.g. constraints). Taking the reader through all of the influencing forces that are architecturally significant will eliminate options hopefully culminating in one architecture being the right one which is the one you have documented.
As you are documenting your architecture be sure to constantly asking if what is being documented is architecturally significant.