Agreed. IMO it's always a good idea to document design choices.

The owner can write down the problem, a few solutions that were considered, why they were chosen/rejected, and a more detailed description of the final design. Stakeholders then review and provide feedback, and after some back and forth all eventually sign off the design. That not only serves to align the organization, but to document why things were done that way, so that future hires can get a sense of what is behind the code, and who was involved in case they have more questions.

This was how we did things at some $BigCorps and it paid dividends.