How are the Database System Events used?
The Enterprise module depends on the Scheduled Jobs and Events module to do kick off the promotions, deployments, cache invalidations and solr incremental updates amongst other things. Users can also plug into it and create their event factory/consumers.
More information on the System Events can be found on the Scheduled Jobs and Events documentation. Looking through this and some of the tutorials on there is the best way to get familiarized with how the system works.