I wrote my first novel, Cadence Beach, without an outline, but as I write this second novel, I find I could use an outline.
I'm not a fan of rigid or long, involved outlines by any means, but I have come to a place in my writing process where I do believe an outline that offers a clear path to follow from point A-Z is a necessary tool. If only I'd come to that helpful conclusion thirteen chapters ago, I wouldn't be limping through my first draft as much as I am. But, as I mentioned, I made it successfully through novel number one without an outline; I'll make it through the current one.
I do write a brief summary or synopsis of a story before I begin draft number one, but I'm finding it's not helpful enough to carry me through to the end. So, my advice to fellow writers is to always write some sort of outline, long or short, for the simple value of moving the process of writing a first draft along at a more reasonable pace. You'll groom the path along the way with adding and changing details , but at least with an outline there is a path to follow.
Through both personal experience (as mentioned above) and a wonderful, helpful book I purchased called Outlining Your Novel: Map Your Way to Success by K.M. Weiland, I'm on my way to a smoother and better paced writing experience. I hope you find the same successful outcome.