Before I had any specific ideas for songs, I had some general musical notions, one of which was this thing. The first idea I put to paper for this project never got anywhere near recording—I thought about it some in the first couple of days and then completely forgot about it.
The staff paper is very handy for recording specific musical ideas. I don't read or write music notation very quickly—can't sight-read, certainly—but it's worth it to fix specific ideas on paper before I forget them or mutate them beyond recognition in my attempts to remember them while doing other things.
Sometimes, I'll even scratch wobbly five-line staffs out on scrap paper if I need to remember a specific idea; so this notebook was a big help, giving me a ready canvas and saving me the effort and distraction required to generate staff paper on the fly.