Planning is always a good idea, I think.
Some writers claim not to plan in advance, but then they are, one supposes, figuring out a functional plan (Hero's Journey, or whatever), as they go.
Um, no. I know this is really hard for the planners to comprehend, but some of us do write with no plan for where the book will go. I don't follow any journey, I don't have a format in mind, I literally start writing. I often don't know if it'll be a short or a novel, what tense it will be, who the main character is. In fact, often I start with the tone that Phyrebrat mentioned recently and nothing more. By the third draft, I will have an idea of the journey and will start to plan a little more, but in that first rush of words nothing is in my mind other than sticking enough down in draft form (usually about a third of the eventual length) that I can hone it. And for that draft, it's a splurge of words and a journey that I hang on for and nothing more.
Whilst being contrary, my first novel/trilogy was a rehash of an old idea. I did start from scratch, but the idea had been around a long time, and it worked fine. But it really did have to start from scratch.