When exporting complete projects, jobs..., you can selectively exclude/include object definitions from the output.
When you exclude the datastore (and do not use Exclude tree!), the datastore settings will not be included in the output (e.g. .atl file), the underlying table/view definitions will. This approach is often used when one wants to avoid overwriting user names and passwords on import in the target environment.
Note that selective import is a new feature of DS 4.2 SP6.