It can be argued that all works of fiction need some sort of planning. Otherwise you get novels without a coherent plot or any sort of ending. (Stopping is not the same as ending.) Very few authors can make that work. Douglas Adams is a noticeable exception that kind of proves the rule – but then, the disorganised way he wrote the original radio play is rather well known. So everyone else must plan to some extent.
However, new writers find full-on planning to be understandably daunting. NaNoWriMo tackles this problem by encouraging people to “just write”, explaining that you can do wholesale rearrangement of written scenes, re-assignment of characters or even re-writing of whole scenes afterwards. This has the advantage of breaking the block of “I can’t write that many words!”, but doesn’t do away with the need to plan. It’s just that the planning is somewhat retroactive.
But that works for some writers. I’ve written several short stories from start to finish with no more planning than an interesting idea and some light editing as I go. And I’ve read some notes from other authors who also write like that. It basically puts all the planning into your head. Non-writing time, like having a shower or taking a walk, is where the planning occurs. And some writers can do this for a novel.
However, I don’t think I’m one of them. My ’09 NaNoWriMo novel is languishing at 38,000 words. I think it’s about halfway through. It started with a couple of vaguish ideas, some rough character outlines and a setting. But managing the plotline and hidden details has gotten too much and now I need to do some planning to make the second half work. So I’ve started a smaller work, again with an interesting but more well-formed idea, and a scene to start things off. At the moment, it is finding character interaction that makes my characters appear, and so I needed that scene written first. Using it, I now have a variety of characters and their goals are coming in to focus. I even have an idea of a climax. But then the really hard work begins: building a plot outline. It will be a learn-as-I-go exercise.