In 7.4, any new tables that you add to CustomerData are added as non-Pega formatted tables and you cannot move pega formatted tables to it. If you create any table from AppStudio, it will be created in customer data.
The purpose is that it brings CRM core data types into your application and also to store records of custom tables created during the development.
However as explained in above post, properties defined in Data Type are exposed anyways, then from performance perspective it does not make any difference. If that is correct, then why exactly was this introduced? The need is still unclear to me.