How to understand the Purge People feature in EngageOne Digital Delivery formerly eMessaging

Product Feature: Utilities
Information on the Purge People feature:
The table stores the information of Unique email ids and is associated with inbound msgindex_people, msg_index and workflow_item tables directly or indirectly. It will store the information such as  customer id, user name, mobile number, etc related to a person identified by the mail address.
Purge will delete all those records which are not having references to above other tables and have expired the set days period (this happens when records from other tables gets purged).
The records have a direct relation to msgindex_people table which in turn has relation to workflow_item and msg_index tables.

More information form EMSG documentations.
Page 147 in the EMSG Reference Guide. 
The purpose of the 'Purge people' is to delete records in the People table where the Date_Modified field subtracted from current system date is greater than the days specified in the Purge_People value in the Vendor table. 
Page 116 in the EMSG Installation Guide 
Purge People in Vendor Environment Page. 
Sets the number of days to keep unused message recipient data in e-Messaging. Enter "0" to store unused data indefinitely. 
UPDATED:  November 7, 2017