Dimensions do not have to be defined.
However, if your application uses dimensional modeling, it is worth spending time creating them as it can yield significant benefits, because :
- they help query rewrite perform more complex types of rewrite.
- they are beneficial to certain types of materialized view refresh operations.
- They are mandatory if you use the Oracle Database - SQL Access Advisor (Summary Advisor)
They are only mandatory if you use the Oracle Database - SQL Access Advisor (Summary Advisor) (a GUI tool for materialized view and index management) without a workload to recommend which materialized views and indexes to create, drop, or retain.