[iamalexm]

Design docs are great for high-level orientation. If you are laying out all your code structure around it, you are doing it wrong. It's great to use the for what patterns will be used (using a facade pattern for example). It gives eng's a guide to how to implement at a high level and it should identify points of non-functional requirements; speed requirements, monitoring, security, etc. Throwaway code doesn't even touch on that. It should also put in scope some of the architecturally significant decisions that need to be made. While throwaway/prototype code can address some of that, it doesn't always identify it and talk about _why_ it is important.

In short, doing both is the best thing you can do and you should scope your design docs correctly.