I can't speak for Claude, but in Codex, plan mode is very useful for finding serious issues with one's spec. I use it to improve my spec. I keep rerunning plan mode over my updated spec until it stops finding issues. It is only then that I execute the spec.
OutOfHere · · focus · HN ↗
LeoPanthera · · focus · HN ↗
dancechess · · focus · HN ↗