I migrated 1==>4
I started with one library, for research documents. I’m now up to 4+
Research documents for all my research projects. This one is large and unwieldy - interesting material sometimes gets “forgotten” because it’s tucked away in a folder I created years ago. So I do a lot of fulltext searches.
Each major outside consulting project gets one. This allows me to encrypt them with separate keys, and leave them invisible except when I’m actually working on the project. It also helps to keep straight who provided me with documents - no danger of using A’s documents on a project for B, unless I make a deliberate decision that they are not confidential.
Personal documents e.g. financial records, instruction manuals for devices I own, and hobbies. Hit that F1 key on every relevant web page! (Not literally - I usually store as PDFs rather than web archives.)
I’ve just started one for teaching material. This overlaps with research, but it’s much smaller, so I can scan through it fast to remind myself of old material that might be relevant to my next class.
The basic value of this approach is that it’s faster to search and scan for relevant material. Also remember that it’s much easier to COMBINE DBs, than it is to split one in half. Breaking things up this way has some drawbacks, notably that I sometimes have to check more than one. (Since, obviously, the specific topics have some overlap.) But when I decide a document is going to be used in several ways, I just copy it into the other database.
One other trend: I use EF more and more for files that used to be handled in the Finder. Hope this helps. I also asked this question when getting started, and I’ve “evolved” into this solution.