Not OP, but I think they're way more essential with AI doing a lot of the coding. The biggest thing that AI, even the frontier models, is not great at is staying on topic and actually finishing a project with reasonable priorities instead of ratholing on insignificant details or claiming it's "finished" when it's half done.
The most important thing that a good design doc does is specify what's in and out of scope. The second most important thing is to precisely define common vocabulary - what are the important concepts in the problem you're solving, and how should they relate to each other? All of that information serves to ground the day-to-day work in what's important. I find myself starting every Claude session with "read this doc and get familiar with the world, then we'll get to work on a part of it".
(The same is true when working with humans, especially but not limited to junior engineers who aren't used to managing a project longer than a week or two. AI coding agents just never grow out of that phase.)
For an entire project? Yes I agree. For a feature or a submodule? I think when you work with claude to develop a plan, it's generally pretty good.
I guess my question stems from being rigid how a design doc should be defined, argued over, and then executed by humans. I think some of the details simply don't matter, and if they do, they often can be changed relatively quickly in order to adhere to the new requirement.
The most important thing that a good design doc does is specify what's in and out of scope. The second most important thing is to precisely define common vocabulary - what are the important concepts in the problem you're solving, and how should they relate to each other? All of that information serves to ground the day-to-day work in what's important. I find myself starting every Claude session with "read this doc and get familiar with the world, then we'll get to work on a part of it".
(The same is true when working with humans, especially but not limited to junior engineers who aren't used to managing a project longer than a week or two. AI coding agents just never grow out of that phase.)