What do you do with semi-used notebooks?

I have a small notebook (the ones that fit in pockets) that I used for taking notes on high school subjects, about 20≈30 pages used, but I didn't ever open It for, I don't know, a year or two, and I'm considering using It for journaling

Do you feel weird about using "random" places for journaling? I feel weird in both ways, either because I'm opening a notebook with biology and physics notes to write about my day, either because I can't use It for that "academic" purpose anymore, It's hard to organize that type of notes on paper, even harder to find a specific one (I organized a Obsidian Vault for that and It feels great yet)