It depends on the book and it depends on how quickly you want to finish it. With my historical novels, (Fever 1793 and Chains) I have to outline carefully because the character’s journey has to take place within real historical events.
With my YA novels, like Twisted and Speak, I am more flexible. In the early drafts, I write whatever weirdness pops in my head. In later drafts, I sort through the chaos and try to give it structure and a sense of flow. But what works for me might not work for you. Everyone has their own process.