Plan mode is critical in the beginning, because there's a lot of long tail decisions that haven't been considered, let alone resolved.

But as skills and memory are populated over time, Plan mode isn't as necessary. It becomes simpler to let Claude just build and get something general in place that works, and then refine from there. Auto mode will ask essential questions.

I still use Plan mode for big feature changes, to confirm that I've asked for what I want in the right way. I tend to prompt casually, with only a few specific details. Plan mode helps me see the whole picture before committing. In a few cases, it also helped me decide the feature I asked for was wrong.