It can be handy to keep your uploads, or, say /var/discourse/shared/web_only on network storage. You need to edit the yml file to point to it rather than use a symlink (the symlink doesn’t work because the container can’t access the place that your symlink points to.
Then if you do move to a new vm, you can just remount that network storage rather than copy it over.
I don’t recommend network storage for the database since it’s slower.