The new General Data Protection Regulation (GDPR) entered into force on 25 May 2018. It includes the right to a complete deletion from your corporate database. You face severe penalties if you don't comply with the request for a complete deletion or only do this partially.
Salesforce has provided a solution for the Marketing Cloud that enables deleting or blurring of contacts from all system tables and all sendable data extensions.
In order to also eliminate non-sendable data extensions, we, factory42, have developed a free solution for you as an extension of the Salesforce tool, which enables a complete deletion of the data.