I too know of people who love to just dive straight into writing code, but I completely agree that at least some form of planning upfront is worth it.
It’s very much like writing unit tests: by writing them, it makes us think in different ways that the system could operate. As a result, we might include additional handling for different use cases that we may not have otherwise thought of. The same is true with a project plan too.
When it comes to system design, I also think it’s helpful to draw up some diagrams. Architectural diagrams help with design and modularisation, and sequence diagrams can show how the systems will communicate with each other.
Once we have those, we have a clear direction and (as mentioned in the article) can move much faster as a result.