Data reduction is used to determine which data a user is allowed to see: all of it or just parts of it?
The data reduction functionality is based on the concept of section access, which is a way to dynamically change which data a user can view. This makes it possible to build apps that can be used by many users, but with different data sets that are dynamically created based on user information. The reduction of data is performed by the Qlik Sense Engine Service (QES).
The definition of access rights for section access is maintained in the apps and configured through the load script.
See also: Managing security with section access