I did once have segregated Calibre libraries. One for cookbooks, one for technical books in PDF and one for 'regular' books like novels and nonfiction in EPUB.

I did once have segregated Calibre libraries. One for cookbooks, one for technical books in PDF and one for 'regular' books like novels and nonfiction in EPUB. The only reason I had it like that was so I could sync just the cookbook files to another device via Syncthing, or only the technical books. It didn't last, it was a pita to manager (three different auto-add folders) and I reunified them after 9 months or so.