After purchasing a sketchbook that really doesn't suit me, I decided to use it as a practice book for people sketches. Now I have a building book and a people book. Oh, and the folding train book too.
Multiple books bothered me before because I was focused on which media to use where and when. Switching the focus to subject matter feels good, especially since I really need to work on buildings and people. We won't discuss other things on which I need to work. The train book is more of a line-drawing and colored-pencil book with my model trains as the subject.