|I can't promise to stop buying them...|
My main use for notebooks is organizing (lists, press trip or conference notes, etc), but I also use them in my fiction writing. This is probably less common in the digital age, but pen to paper just makes sense for some of us.
Natalie Goldberg's Writing Down the Bones was written before there was a MacBook on every table at your local coffee shop. This is why many of her tips are computer-free. I found this craft book while cleaning up my bookshelves and decided to reread it. Here's an interesting tip she had about notebooks, and using them as a tool that works for you:
"Sometimes people buy expensive hardcover journals. They are bulky and heavy, and because they are fancy, you are compelled to write something good. Instead you should feel that you have permission to write the worst junk in the world and it would be okay. Give yourself a bit of space in which to explore writing. A cheap spiral notebook lets you feel that you can fill it quickly and afford another."
Fancy notebook syndrome is a drag - I caught it once when I had a BIG IDEA that needed an equally spectacular notebook to expand in. I remember squishing my words so teeny tiny, because I was afraid of using up the pages too quickly. There was a grid pattern on the pages that also distracted me. I wanted my writing to be neat and error-free, like the perfect boxes that lined up and down the pages. Clearly, this was not the ideal blank slate.
Goldberg recommends using something cheap. She prefers notebooks with cartoon characters on the cover as a reminder not to take herself and her draft too seriously. With the right pen, filling up the pages should be the easy part.