For what it's worth, I use two physical libraries. The first is called Intake and is where I import books, clean up the metadata, do any needed editing, etc. Once the book is ready, it gets moved to my main library (called Main since I tend to be boring). In Main, I use several virtual libraries based on various criteria instead of having multiple physical libraries.
And yes, what @theducks and @ownedbycats said about local drives is very true. There have been all too many posts where the poster says something to the effect of "I've had my library in <pick the cloud storage/NAS of your choice> for years and now most/all of my books have disappeared."
Back your calibre libraries up to cloud/NAS/whatever. Just don't run calibre against a cloud stored library.