I believe in research. Having your own personal library often provides you with needed material that helps you better understand a subject for your book. Maybe a critical weapon, a graving tool, or some other item that fits into your story. How about a How To book that covers something you’re writing about?
There was a time when an author only had his own imagination, his experience, and, if so blessed, a dictionary as resources. But the world has changed since those olden days.