Thats a big sometimes for me. I am unfamiliar with the app development process. For backend,I would rather design the whole thing from scratch rather than try to fix a broken architecture. For frontend, maybe that is true, but I haven't had the chance to build anything complex, just forms and tables.
It's much easier to take "well now I have an app, which after using for a bit I find it sucks in <quantifiable list of ways>" and then fix them, than it is to start from absolutely nothing.