In Qlikview it is always advisable to minimize the number of tables in the data model.
Mapping Tables are used in QlikView to clean up the data model.
Tables with just 2 columns can be removed and columns of that table can be mapped to another table.
Mapping tables are stored in a separate area in memory and used only as mapping tables during script execution. After script execution they will be automatically dropped.
Please watch my video for more details
Further readings : Don’t join – Use Applymap instead