I found that minimizing transformations on your data is a principle you apply when you productionize. For most of the development cycle, you want to keep things as debuggable as possible (at the possible expense of performance), and intermediate data products + debugging hooks are a good way to do this.

This brings up a much bigger question of when to productionize, though. Most programs are never actually "done", but at some point you have to release to the public and hopefully get millions of users. You need to make the performance/maintainability tradeoff sometime. The later you push it off, the more productive you can be in the critical early stages, and the better a product you can bring to market. But if you push it off too long, you miss the market window entirely and don't get the benefit of user feedback.