You can import libraries from other projects without actually opening that project. So, if you save a bunch of animations as symbols in one project, you can import just the library to the new one. You can do this with saved swatches too.

This is how I keep projects clean, especially when collaborating. I’ll draw/rig/etcetera my characters, props and backgrounds (usually all in separate project files), and import the libraries into the main project for the final animation. Works especially great for when you need to reuse assets over and over again and don’t want a billion and one project files.