Single library vs. multiple libraries

I’m curious to understand what are the pros and cons of having a single library vs. multiple libraries.

I started out with a library for general filing, one for long-term reference, once for emails etc. Gradually though I moved to a single fixed library as I found it more useful to be able to search in one place and turn up hits that I didn’t expect. I generally use folders and tags to sort within that single library and will probably stick with that model as it seems to swallow up everything I need.

I suppose the compromise would be to have an inbox for grabbing thing quickly and then another library for longer term storage. Any further thoughts?

Until very recently I was using a single library. However when doing library-wide search, including email messages, things would get a bit slow. (My library was pretty big: about 14GB, 5000 records, 52000 emails.) So I’ve started moving some things away in an “Archive” library, for older stuff. The drag&drop between libraries is very convenient, and I have not had trouble finding things when I need to.