It depends a lot on the context. Richard Stallman defines hacking as "playfully doing something difficult, whether useful or not". In the context of hacking, change for the sake of change is perfectly fine. You don't always have to move forward and get things done. Leave that for the corporate world where your goal is to make money. Many of us have learnt a lot just by switching programming languages many times and rewriting stuff. We're not losing time, we're learning in the process, and most importantly, we enjoy it, because that's what hacking is about.