Given an initial set of records to delete prune_ar deletes all other records (accessible via ActiveRecord) that are now orphaned due to a belongs_to relation which is now non-existent. This allows you to safely delete records that you want to delete without creating orphaned records in another table (& without violating foreign key constraints if you use them). This can be used to prune a production database (given deletion criteria for top level parent-less independent entities) for use in a development environment without compromising customer data.