This is where I store excerpts and quotes from things I read. It's a commonplace book aiming for cross-pollination in as many ways as possible.
I used to store everything first (many years ago) in a paper book, then in a Word file, then a Google Docs file, and now using obsidian.md.
The local file gets updated roughly weekly, when I finish a book. You can read more about its creation in this article.