For a solution architecture to be of utmost value it must address the target business capabilities in a manner that is maintainable, extensible and scalable. Solution Architectures follow unstated core drivers that influence the focus of the approach. The most common of these drivers are (in order): Initial Cost, Vendor Capability, Total Cost and Business Capabilities. These drivers are not mutually exclusive, and the key driver will be what each of the other drivers are weighed against in the solution. Each driver has value to the project and the enterprise as a whole.
In my opinion, Business Capabilities is the best key driver to have. Business Capabilities are what support growth and sustainability and contribute the most to the enterprise. The other drivers should not be completely sacrificed, but when they are given priority the result is frequently a gap between actual need and provided solution. They are driven by agendas that are secondary to the overall enterprise needs and better kept in the corresponding secondary priority.
This is not to say that every business capability requested by an individual or group is valuable to the enterprise as a whole. The business capabilities to focus energy and resources on needs to be carefully chosen by the business, and once identified as a core need of the enterprise should take its place as the key driver.