Starting with Site Studio 6.8.0 a new package management system has been introduced; this changes the way a user exports and import packages including several different options when used via Drupal UI and Drush CLI. As a result the previous system has been marked "legacy".
In Site Studio 6.9.0 further features for importing multiple packages at once with a single command or via custom code solutions have also been added. With this change a deprecation message has been added to Drush CLI, informing users of upcoming changes when using the legacy commands.
We recommend users move to the new packaging system to benefit from the performance improvements and to be ready ahead of the legacy system being removed in a future version.