I do it all the time.
The truth is that without my notes it’s like I am blind. They are my map and guide me step by step from the beginning until the end of my novel. So far I have two separate notebooks for my two novels and I keep them with me all the time. I feel like the Gollum from the Lord of The Rings some times. They are my precious! If someone will look through those pages he will see my stories unfolding before his eyes, so I keep them hidden. I don’t want for someone to learn the end before they have the chance to read the book, right?
To the point, let’s talk about the notes. When I started writing my first novel I wanted to be organized so I could build a solid story and not leave anything behind. As we know “A good book never tells its secrets at once” and so I had to build mine and stick to them, revealing them drop by drop but not miss anything. I took a notebook and I wrote down all the info about my characters, their descriptions, ages and other stuff I thought they were important. The next step was to write a synopsis of every chapter. That helped me to look the bigger picture and plan the next chapter and then the next after that. As a result it became really easy for me to continue my story even if I had to write for days and having everything in plain sight, made it easier to “play” with the story.
Later, I started writing things I was planning to write, some ideas of what it could happen and I gathered parts form the story that helped me. I even wrote whole chapters during times I wasn't at my computer. Some things form my notes never make it to the actual story and other I had in mind never make it to the notebook, but the fact is that my notebook was my compass through the months I was writing the first draft.
I don’t know how it works for you, but I guess that every writer keeps notes and everyone has its own system. For me it is a notebook where between its lines I find random thoughts and make them a story. Want to tell me yours? Leave a comment and I am happy to discuss it.