A planning phase is essential to the product development timeline. Having a good idea of budgetary needs, timelines and deadlines to meet, and team member duties is necessary for success. However, I like the idea you bring up, things change. Throughout the development process, things change and the schedule and budgets might need to be adjusted. Like mentioned, this doesn’t necessarily mean that it is taking a step backwards, or losing time on the project. In order to continue to make good progress in development, there needs to be an accurate timeline and plan, if work from the planning phase needs to be adjusted in order to compensate for this, so be it, overall it will prove to be worth the small delay in the long run.