As far as managing requirements (from Strategic Needs, and oriented towards outcomes) through to delivery the RTM is the end-to-end tracking tool. However, it relies upon the creation of the other documents to track requirements through the process.
“Specifications talk about the need, not the solution.”
Another important thing to consider when looking at design principles is ensuring that all appropriate voices are heard through the proper identification of, and discussions with stakeholders. If stakeholders aren’t consulted about their needs, their needs are unlikely to be effectively addressed by and solution design. Another aspect to design management is change management. Change management is a formal process of introducing change into the scope of the project. Change management against design items is a subset of the change management processes described in the Scope Management topic.
Writing up designs gives stakeholders a chance to read and agree to them, or to highlight any gaps that they see. This usually requirements more than a diagram or document, and in my experience facilitated communication works best (ie a presentation or workshop about what is actually being described in the document.)
The RTM also provides a simple and powerful tool to track what needs/requirements are being addressed at each stage of the development cycle. The use of an RTM works best when there is a clear development process that all project participants are aware of.
I can’t think of any weaknesses in relation to having a design principles and a good control process in place. Again it seems like a very natural thing to want to do.
I suppose that the key thing to ensure that design management principles are effective is to ensure everyone knows what they are and why they are there, including the people controlling changes. Changes aren’t bad, and in many projects there has to be changes to ensure the client gets a satisfactory result.
Thinking about this topic presents me with an opportunity in my work practices. I want to ensure that in future I communicate the design principles and process that we will use to the stakeholders, and not assume that they know what we are doing and why. The threat in this area comes from people who do not know why certain processes or practices are being followed; and again the answer is communicating.