The best use of the export command is for backup or copy of an existing project's content into another project.
Technically, exports aren't exports of projects - but rather they are exports of Branches. You could export the master branch from one project and import into the master branch of another project. For example:
1. export the content to the vault
2. create a new project (using CLI)
3. import the content from the vault to the new project
You can then import this on top of the branch with the full set of imported content. Any nodes included in the ZIP will either newly create or merge/update with existing nodes provided that their QNames match. Folder paths and things work themselves out as do definitions.